The following correction was printed in the Observer's For the record column, Sunday August 15 2004

Readers tempted to follow advice given in the article below to move their washing machine from kitchen to bathroom should contact the manufacturer to ensure that the appliance is suitable for bathroom installation. The electricity supply must be protected by a residual operating current. Contact the Electrical Contractors Association (ECA) for further advice or visit Eca.co.uk.

On the day of Jenny Morris's visit, our kitchen is inexplicably filled with flies. I say inexplicably, but as Jenny - the doyenne of food safety and hygiene - is about to tell me, no unwelcome visitor to the domestic kitchen is there without an invitation from a slapdash cook. It's the hottest day of the year and the back door and windows are wide open. Something must be luring the flies in. 'That bin is the problem,' Jenny observes in her matronly, Margaret Thatcher way, inspecting the US-style trash can (Jerry's Home Store, circa 1995) with its letterbox lid hanging limply open and a disposable nappy clearly poking out the top. 'It's not just that the spring is broken, but you have to touch it every time you throw anything away. Your hands pick up bacteria and transfer them to food, which is why you should wash them regularly. A pedal bin is better, even if it's less fashionable.'

I can see where things are heading. Here I am, confidently inviting an environmental health officer (EHO) to watch me cook, secure in the belief that our kitchen is pristine and my culinary habits impeccable - and already I have failed. 'What shall I do about the flies?' I ask flatly, expecting Jenny to recommend Vapona fly-paper strips or a repellent device - but her solution is low-tech. 'Give all kitchen surfaces a good wash down before you start,' she says, 'using hot soapy water. That should be done every time, regardless of the weather. After that, don't leave out any food on which flies are likely to settle; if you do, cover it.'

It's a sobering thought, that no meal should be prepared without scrubbing up like a surgeon and scrubbing down like a deckhand - but that is the reality of cooking in a British summer. July and August are peak months for cases of infectious intestinal disease (IID), characterised by diarrhoea, vomiting and abdominal pain, and passed from person to person. The condition accounts for 10.5 million cases a year and costs the country £750 million in healthcare bills and lost working days. Of these cases, perhaps 2.4 million are directly caused by food poisoning and, in particular, fly-borne bacteria. Feeding alternately on filth (notably faeces) and sweet foods (such as sugar and milk), houseflies regurgitate their first meal on their second, trample it to a slurry with their feet and siphon it up, leaving behind bacteria trapped among their leg hairs. 'You never know where flies have been,' says Jenny, 'so you don't want to take any risks.'

Nor is it just insects that are at their most active in the warmer months. Thanks to inept barbecuing (which leaves bacteria alive in undercooked meat), mass outdoor catering (which spreads infection), poor personal hygiene, defective refrigerators and rapidly deteriorating food, the bacteria associated with poor animal husbandry also have a field day. Farm animals harbour organisms in their gut which are spread to the outside of meat at the time of slaughter; eggs and milk can also be tainted by the disease and fecundity of the farmyard. In August, cases of salmonellosis (caused by the salmonella bacterium) increase fourfold compared with January, while campylobacteriosis (from the campylobacter bug associated with poultry) doubles. Though both organisms can be killed by thorough cooking at high temperatures, they can be transferred to foods such as salad which will not be cooked - typically when the juices from raw meat and poultry drip onto the shelf below in the fridge. This is cross-contamination.

So significant is the problem that the Food Standards Agency has set itself the target of achieving a 20 per cent reduction in food-poisoning cases by 2006, focusing its campaign on five micro-organisms that are rampant during the summer months: salmonella, campylobacter and clostridium perfringens (responsible for the largest number of cases) and listeria and E.coli 0157 (which causes more severe illness in fewer people). In June, the Food and Drink Federation - assisted by the FSA and others - ran a National Food Safety Week highlighting how bacteria are spread. 'Are You A Chicken Splasher?' its campaign literature asked, referring to a finding that 81 per cent of Britons rinse poultry under the kitchen tap before cooking it, splattering bacteria over sink, work surfaces, utensils and themselves.

'That is classic cross-contamination,' Jenny Morris explains, 'which is one of the Food Standard Agency's four Cs [used in its campaign as an aide-memoir for avoiding food poisoning]. The other three are cleaning, cooking and chilling.' It is against these criteria that my performance will be judged by Jenny (who, as well as being an EHO, is policy officer for the Chartered Institute of Environmental Health). To make things worse, I have chosen ingredients and methods notorious for their food-poisoning potential: frozen scallops, king prawns, fresh raw tuna and cod, sliced, marinated in lemon juice and threaded on skewers with red and yellow peppers and courgettes. These kebabs will be lightly grilled (to simulate barbecuing) and served with new potatoes and a salad of organic red batavia lettuce, Little Gem leaves, wild rocket and vine tomatoes. My pact with Jenny is that I will behave as I do when preparing a family meal; I must not sanitise my technique on account of her presence. Armed with a probe thermometer and a critical demeanour, she will judge my food safety and my personal hygiene.

First, there is the bacteriological can of worms that is our fridge - an ancient, leaking Hotpoint bought for £20 from the previous owner of the house. 'I'll just leave the thermometer in here for a while,' says Jenny, as I pick up an abrasive sponge - our only abrasive sponge - and begin scrubbing the new potatoes. Wiping down the board I chopped them on, I take my medley of fish and seafood from the fridge, where the scallops have been defrosting overnight. I can see Jenny taking notes. A quick slash with the knife, a squeeze of lemon juice, some salt and pepper, and the fish and vegetables are ready for assembly on skewers. Brushing the kebabs with olive oil, I stick them under the grill and start preparing the salad. Jenny takes her thermometer from the fridge, looks at it through narrowed eyes, then sticks its probe into a can of tuna covered in Clingfilm, leftover from the night before. She closes the door and retrieves the thermometer later.

Oddly, like the unprecedented flies, the grill undermines my confidence on the very day I am being held up to scrutiny. Our gleaming Smeg cooker which we cherish like a baby (even using Johnson's baby oil to maintain its mirror-like sheen) takes nearly half an hour to grill one side of the kebabs. There is plenty of time to chat. I discover that Jenny has been both a chef and a caterer before becoming an EHO - so my meal will be judged for its culinary merits as well as micro-biologically.

'It's all very tasty,' she says politely at my hour of reckoning, when we eventually sit down to a plateful of pale, fashionably underdone kebabs and a fly-blown salad. 'I haven't seen anything so bad it makes me not want to eat it.' Without warning, she whips out her thermometer and thrusts it deep into a scallop, retrieving the device after two minutes. Is it my imagination, or does she look worried? 'It's 59 ,' she announces, 'but to kill all the bacteria you need to achieve 70 at the centre for two minutes. Wouldn't it be good for your story if we both went down with food poisoning?' I laugh nervously.

How the bacteria stacked up

Chopping boards

Upside: mine is expensive and constructed from a single piece of wood. 'Those made from several pieces are glued together,' says Jenny, 'and if the glue starts to give, you have lots of gaps for food-trapping and bacteria.'

Downside: although there are two boards in the house, I am too lazy to use the second. The same one is used for raw fish and seafood as for chopping vegetables and salad, albeit with a good wash down in between. Theoretically, I turn it over when I switch from raw fish to vegetables - but I can't recall which side I'm on. It's a perfect recipe for contamination.

Remedy: 'In a domestic kitchen, it's a very good idea to have more than one board,' says Jenny, 'ideally in different shapes or colours, so you can differentiate. Anything "dirty" - raw meat and fish - would be prepared on one, and all the "clean" stuff - salads and sandwiches - on the other.'

Commercial food businesses use heavy-duty plastic or polypropylene boards, which are the most hygienic, and Jenny recommends them. 'If you have only one board,' she advises, 'spray it after use with a sanitiser, an antibacterial spray such as Dettox, then wipe it dry with a piece of kitchen towel. Because the risk of cross-contamination is so high, I might not rely on hot soapy water.'

Cloths and sponges

Upside: there really isn't one.

Downside: 'It's one of your big failings,' says Jenny, witheringly. 'You have a major cross-contamination issue with your cloths.' To begin with, I used the same abrasive sponge to scrub muddy potatoes as I did to wipe down the board on which I prepared salad - spreading farm bacteria everywhere. Then, after chopping raw fish and seafood, I used the same sponge again to swab down kitchen surfaces. 'Even though you rinsed it out,' says Jenny, 'it has potential bacteria traps because it is abrasive.'

That was certainly the finding of a University of Westminster study examining the fingertips of subjects after using different types of cloth: for a sponge, the count was 65.8 colonies of bacteria on the fingers compared with 39.7 for a dishcloth and zero for a paper towel. Some 83 per cent of sponges examined showed a 'high' rate of contamination after one day's use (with more than a billion bacteria present, rising to 10 billion after several days). As the study's stomach-churning summary pointed out, the source of bacteria 'varied from water to the human gut, respiratory tract and skin' and included E. coli, salmonella and the distinctly unappetising enterococcus faecalis.

Remedy: use different cloths or sponges for different tasks - 'That's my clean cloth, the yellow one; that's my dirty cloth, the blue one,' suggests Jenny. Failing that, boil, bleach or disinfect cloths regularly (ideally every day) or throw them away. Non-woven dish cloths are better than sponges because they have fewer 'traps' where germs can hide, and hold less water, which helps bacteria thrive.

The freezer

Upside: everything in it is still frozen! The scallops were defrosted in the fridge, not the open air - 'the correct way to do it', says Jenny. 'A lot of research has been done on defrosting,' she explains, 'and the recommendation is to do it in the fridge, where there are controlled conditions.'

Downside: I didn't check whether the scallops were thawed right through before using them. 'If that product is not defrosted at the core,' says Jenny, 'the little nugget of ice in the middle will cool the scallop down and stop it cooking properly.' The result: serious food poisoning. I also splashed water from the scallop bag on to the kitchen surface - a cross-contamination issue - and put the unsealed bag back in the fridge next to a tub of hummus. 'Those juices can contaminate other things,' Jenny warns.

Remedy: press defrosted food with your fingers to check it is thawed, or even run a skewer through it. Be careful with defrosted juices, which carry bacteria.

The fridge

Upside: to my amazement, Jenny gives this a clean bill of health. 'You've got reasonable separation,' she says, 'with your salad on the top and your meat below to avoid cross-contamination. Everything was covered properly and it gives the general impression of being clean.'

Downside: a fridge should operate at 1 C to 4 C to stop bacteria multiplying - but this one registered 9 C on Jenny's probe thermometer (after the door was opened briefly). A better indication was the tinned tuna, with a core temperature of 6.7 C. 'You are just within the legal limit for commercial premises, which is 8 C,' says Jenny, 'but the general safety recommendation is 5 C and below.'

Remedy: buy a new fridge - or at the very least, a fridge thermometer. Turn up the temperature control in summer.

The grill

Upside: it certainly looks attractive.

Downside: it doesn't work. Maybe I omitted to turn it on fully, but it took an eternity to cook the kebabs. 'The danger with that,' Jenny points out, 'is that if something has been under the grill a long time, people assume it is cooked and don't check.' She checked, and found the core temperature of the fish was 58 C or 59 C. 'To make sure you have killed all the bacteria,' she warns, 'you need to achieve 70 C at the centre for a minimum of two minutes. The cooking temperature depends on the food product - and if that was a piece of chicken [notorious for bacteria], pork [known to contain parasites] or a burger [where the mincing process transfers surface bacteria to the core of the patty], you would have a potential problem.'

Remedy: if the grilling is suspect, as with a barbecue, it's essential to cook very thoroughly. No fashionable pinkness, says Jenny, and no 'piercing with a skewer until the juices run clear'. That method, she found as a caterer, is far too subjective and it's better to cut through to the centre of the meat with a knife to check. Chicken, she argues, should never be served at a barbecue. 'Don't do it,' she says, 'because you can't cook it properly on account of its size. If you must, cook it in the oven and finish it over charcoal.'

The hands

Upside: there is a bottle of antibacterial hand-wash by the kitchen sink.

Downside: I never use it. 'I'm sorry,' observes Jenny, 'but you really don't wash your hands very often. You should definitely wash them before you begin and after handling raw fish or meat - but you didn't.' From fingertip to elbow, the average person has between two million and 10 million bacteria, according to Martin Paterson, deputy director general of the Food and Drink Federation. 'If you wear a ring,' he adds, 'there could be as many germs under it - 700 million - as there are people in Europe.' No wonder Jenny recoiled when I failed to wash my hands after assembling the (raw) fish kebabs. 'You went to find your oil brush,' she says, 'and you rooted through the kitchen drawer, touching many things. The handles of your utensils are now contaminated, the drawer handles are contaminated. Then you picked up your oil bottle, so the next person who touches it will pick up that contamination. They may be handling a salad next.'

Remedy: wash hands regularly and do it properly. Most people neglect to clean around the thumbs, between the fingers, and around and under the nails, and the hands should be vigorously rubbed together for 15 seconds. Wet them before applying soap and dry them on kitchen towel: 1,000 times as many germs are spread from damp hands as from dry.

The kitchen

Upside: 'It looks clean,' Jenny pronounces. 'Nothing made me gasp in horror.'

Downside: the designer swing bin, with its lid flapping open and all kinds of fly fodder (including the baby's soiled nappies) inside. Less obvious is the washing machine, sited under food-preparation surfaces. 'Wherever there is moisture there is contamination spread by the aerosol [droplet] method.'

Remedy: 'Definitely get a new bin,' says Jenny. 'Whenever you prepare food, wash down all surfaces with hot soapy water as a precaution; you don't know whether flies have landed there or not. Thereafter, cover all food immediately. And re-plumb the washing machine in the bathroom.'

Knives

Upside: we have a whole range to choose from in our Global knife-block, including - wait for it - a tomato knife.

Downside: the smallest, sharpest vegetable blade is the only one we ever use (except for cutting bread and carving meat) - for fish, seafood and vegetables. 'The biggest issue around that,' says Jenny, 'was the lemon used in the marinade. You sliced it with the knife used for the raw fish and put the remainder straight back in the fridge. That lemon now has raw fish on the edges - so if you use it in, say, a drink, there will be contamination. If it's a gin and tonic, the alcohol might kill the bacteria; if it's a soft drink, it won't.' The result? A bacteria cocktail.

Remedy: ideally, use different knives for different foods. Failing that, wash the knife thoroughly when going from meat or fish to food you will eat uncooked. 'I'd probably use the sanitiser spray again,' says Jenny.

Leftovers

Upside: 'This was fine,' says Jenny. (I'm usually such a pig, there are none.)

Downside: 'You need to think carefully about what you are going to do with this food afterwards.' It is very important to cool food down before it goes back in the fridge; the maximum recommended time is 90 minutes, after which it will attract flies and be at a perfect temperature for bacteria to multiply. Quick cooling is an art. 'If it's a great big container of stew left over, split it up into smaller bowls,' says Jenny. 'Instead of cooking a single large joint, have a couple of smaller ones or cut it to aid cooling.' One major problem is rice. 'There is a bacterium associated with it, bacillus cereus,' she explains, 'which has a nasty habit of producing spores when conditions are adverse. It is very resistant to heat.' When cooked rice is left in less than ideal conditions for four or five hours or overnight, spores are released and the bacteria multiply dangerously. Though associated with takeaway restaurants, bacillus cereus might be a problem when making rice salad - leaving cooked rice in the open air and making the salad later. People will eat that live bacteria.

Remedy: 'The best way with rice is to cook it and eat it quickly,' says Jenny. 'If you want to re-use it, cool it very quickly and refrigerate it.' Some people do reheat rice successfully - that's what fried rice is - but it's safer to throw it away.

Tea towels

Upside: see cloths.

Downside: a cross-contamination disaster area. Tea towels hold a special place in the pantheon of food-poisoning risks, being damp, laden with bacteria from hands and decomposing food and typically kept on a warm radiator where bacteria thrive. 'A few years ago,' says Martin Paterson, 'we [the Food and Drink Federation] were highlighting tea towels because they are a major carrier of germs. People would go for six months without washing them; they'd just leave them sitting around on work surfaces. They are a huge source of contamination.' Jenny Morris also had a few things to say: 'I've noticed that you dry your hands on the tea towels,' she says. 'Again, you are transferring contamination on to those tea towels, and then you are using them to wipe down the chopping board you've just cleaned. You have possibly re-contaminated the board and the tea towels.'

Remedy: 'You should never dry your hands on a tea towel,' Jenny insists. 'Kitchen roll is quite good. Don't use a tea towel on your chopping board; wash it, drain it and wipe the surface with a paper kitchen towel, which is for a single use.' Martin Paterson adds: 'Even for washing up, it's best to leave the dishes to drain, then use disposable cloths or paper towels.' Chuck your tea towels out.

Washing up

Upside: I scored full marks - almost. After washing the dishes in warm, soapy water, I rinsed them in hot water (described by Jenny as 'best practice') and left them on the surface to drain. My wife would never allow this; she says I'm lazy.

Downside: though this is the best method when washing up by hand (because it avoids wiping, tea towels and contamination), it is far better to use a dishwasher. 'They typically operate in excess of 80 C,' says Jenny, 'because at about 82 C, water starts to act as a disinfectant. The heat is killing bacteria, which you can't achieve with a hand wash - even wearing rubber gloves. All the warm water is doing is loosening the dirt and grease from the plate. With rubbing and the penetration of the soap, this might get some of the bacteria off but it certainly won't kill them. What's more, if you don't change the water often enough, very soon it won't be hot soapy water; it will be a bacterial soup.'

Remedy: buy a dishwasher.

Guess whose coming to dinner

Campylobacter

What is it? The most common food-poisoning bug in Britain, responsible for 43,445 cases in 2003 and causing about 80 deaths a year.

Where is it found? Raw and undercooked poultry, red meat, unpasteurised milk, untreated water.

Party trick Very potent. Just a few bacteria in a piece of undercooked chicken can cause severe illness.

Symptoms Gastroenteritis with fever, abdominal cramps and diarrhoea that is often bloody. The most serious cases can be fatal.

Clostridium perfringens

What is it? Officially, the third most common food bacterium in the UK, although the least reported because symptoms are vague and often dismissed as IID (infectious intestinal disease). In 2000 there were 166 confirmed cases but it is estimated that only one in 343 is notified. The real total could be closer to 57,000.

Where is it found? Soil, sewage, animal manure and the gut of animals and humans. It can easily be transferred to poultry, meat and meat products. Foods cooked slowly in large quantities, then left to stand for a long time, are its breeding ground. Particularly associated with leftover gravy and stuffing.

Party trick Clostridium perfringens can't be completely destroyed by ordinary cooking. It produces heat-resistant spores which may even be stimulated by high temperatures, causing the spores to germinate further. Unless infected food is eaten immediately, the bacteria will multiply rapidly as the food cools down. It must be reheated to 'piping hot' (ideally 75 C) to be safe.

Symptoms When ingested in large numbers, the bacteria produce toxins which attack the gut lining, causing diarrhoea and acute abdominal pain.

E.coli 0157

What is it? Most strains of E.coli are harmless, but those producing the poison verocytoxin (VTEC) can cause severe illness. Of these, E.coli 0157 is the most common in Britain. A small number of cases (675 last year) have serious repercussions.

Where is it found? Farm animals and land contaminated with their faeces. Among foods, E.coli is transmitted most commonly through undercooked minced beef (such as burgers) and milk that is raw, inadequately pasteurised or contaminated after pasteurisation.

Party trick The bacterium can spread directly from animals to humans and from person to person.

Symptoms Abdominal cramps and bloody diarrhoea. In serious cases, kidney failure, severe anaemia, neurological problems and death.

Listeria

What is it? Full name listeria monocytogenes, a food-poisoning bug of particular danger to pregnant women, babies and the elderly.

Where is it found? Everywhere in the environment, because it can survive at low temperatures (most bacteria require warmth to thrive). Foods most at risk are soft, mould-ripened cheeses, ptés, unpasteurised milk and shellfish.

Party trick Resists heat, salt, nitrite (preservative) and acidity better than many micro-organisms.

Symptoms Fever, headache, nausea and vomiting. Can be fatal to the elderly, the immune-impaired, infants and developing foetuses.

Salmonella

What is it? The second most common cause of food poisoning after campylobacter (14,853 cases in 2003), widespread in eggs and poultry flocks in the 1980s.

Where is it found? Despite the poultry industry cleaning up its act with new codes of practice and the Lion Quality assurance scheme, salmonella is still found in eggs - at about the same levels as before the Edwina Currie debacle. Other sources are raw meat, poultry, unpasteurised milk, yeast - even pasta, coconut and chocolate.

Party trick Grows very well in the food itself, so a tiny number of bacteria will multiply to thousands of millions if the product is not chilled. Salmonella is also passed easily from person to person by poor hygiene, such as not washing hands.

Symptoms Usually mild, including abdominal pain, diarrhoea and nausea but rarely vomiting.

Scrombotoxin

What is it? Not a bug as such, but a poison produced by certain bacteria present in oily fish which has been allowed to spoil through inadequate refrigeration. It causes a dramatic histamine reaction.

Where is it found? Fresh and tinned mackerel, tuna and, very rarely, Swiss cheese.

Party trick Once produced, the toxin is heat-resistant. Cooking, canning or freezing will have no effect. Contaminated food will not look, taste or smell any different from usual.

Symptoms Tingling or burning in the mouth, a rash on the face or upper body, itching, sweating and headache, accompanied by a drop in blood pressure, abdominal pain, diarrhoea and vomiting may follow.