The last time I was eating dinner here with John Humphrys, both of us were hitting the wine with determination. We needed a bit of Dutch courage for a very good reason: Humphrys was taking me lap-dancing.

A few weeks earlier, a strip club had opened round the corner from his house in Hammersmith, west London. A reporter called him up. What did the great man think of this seedy new addition to his area? A bloody disgrace, he said. Send 'em packing. Flippantly, he added: 'It'd take an awful lot of money to get me in an appalling place like that.'

I took his words at face value. I rang him. 'An awful lot of money?' I said. I mentioned a vulgar figure and asked if he would be prepared to visit the club, interview the strippers and write about it for the newspaper I worked for. The suggestion amused him. 'My partner's away for a few days,' he laughed. 'I'll do it.' But he wouldn't go on his own. We'd have to meet for dinner first and go to the club together. He didn't want to look like a member of the dirty-raincoat brigade.

This time we meet a few days before his recent trip to Iraq, from where he co-presented the Today programme for two days last month. Reunited at our original pre-strip-show rendezvous - Humphrys's local restaurant, the Brackenbury - he insists with a smile: 'You led me astray.' I'm sure I remember it the other way round.

A lot has changed in Humphrys's life since our little escapade. He still lives in the area - though these days in a larger house a few streets away, having set up home with his other half, Val - but now the couple have a six-year-old son, Owen. At 63, Humphrys is relishing his time as a family man this time around (he also has a grown-up son and daughter). He's come to the restaurant straight from his kitchen, where he was making Owen's dinner. Humphrys does 'pretty much all the cooking in the house', but it's the food he prepares for Owen that gives him the greatest pleasure.

'I love cooking for him. The satisfaction of having a child eating your food and appreciate it is enormous. Particularly if you know he probably wouldn't like it if he knew what was in it.' Owen's dinner tonight was 'a very thick soup of carrots, potato, garlic, tomatoes and - here is the bit I was really proud of - avocado. Because he "knows" he doesn't like avocado.'

As one might expect, Humphrys does not have much time for picky eating. One of his son's friends will eat nothing but sausages, potatoes, baked beans and bread, but Humphrys junior would never get away with such nonsense. It's important to expose children to a wide variety of flavours from early on. 'Like curry. He had a curry last night. We made a point from babyhood, once he was on solids, of giving him spicy foods so that he could get used to the notion. And he loves garlic, he really does. And that's a very good thing.' Humphrys uses a lot of garlic. 'If a recipe says use a clove, I use a whole bulb. Because I just think of garlic as another vegetable, like onions.' As a result of the John Humphrys food plan, 'Owen's got to the stage where he'll eat almost everything. But you have to do a bit of concealment.'

For the grown-ups, much of Humphrys's cooking is hearty and classical. He's a self-proclaimed meat-and-two-veg man. At our last get-together, he described to me how he slow-cooks neck of lamb with rosemary (and, yes, a bulb of garlic) in the oven. The recipe sounded delicious and I switched butcher on his recommendation. His cooking methods, though, are not always traditional. If he's making food only for himself - he sometimes eats dinner early, because he gets up at 4am when he's presenting Today - he'll often turn to his favourite kitchen gadget.

'People sneer, but these George Foreman Lean Mean Grilling Machines, whatever you call them ... they're brilliant. You parboil some potatoes, get a few shallots, a piece of decent lamb ... you just coat everything in olive oil, stick it in the machine, and - boof! - 10 minutes later it's done. If you stuck that meal in front of anybody in this restaurant, they'd say it was lovely. A bit of mint sauce. Perfect. And people go on about the effort of cooking! There isn't effort in cooking.'

Humphrys takes his food seriously. Though he derives great pleasure from it, it also makes him angry. And early on in his life, it was clearly a source of worry to his parents, who struggled to earn enough money to feed their large family.

As a result, food plays a very large role in his moral universe. Five times he tells me that it is 'wrong' or 'morally wrong' to waste food. He's been a wealthy man for perhaps three decades, but he cannot - indeed, he would not want to - shed the values he was forced to adopt when food was scarce. And though he has spent nearly 50 years as a journalist, he talks of the middle class with a touch of disdain. He does not seem to see himself as a member of the club. He's also got a rather authoritarian streak. He's surprisingly keen on banning things and wants to use the law to force supermarkets to sell healthier food.

Humphrys was born during the war into a working-class household in Splott, in inner-city Cardiff. He was one of five children (a sixth died aged seven months); his father George was a French polisher and his mother Winifred a hairdresser. When there wasn't enough work, the family was desperately poor. 'There was never quite enough food,' he recalls. Sometimes his father pawned his mother's wedding ring to put food on the table.

What would a typical lunch or dinner look like? 'For a start we didn't have lunch and dinner. We had dinner and tea. And, to this day, I can tell you what we had every day of the week.' Sunday it would be either shoulder of lamb, a cheap cut in those days, or the point end of brisket of beef. The roast and its associated offal would be reheated, re-cooked and made to last three days. Then on Wednesday it was stew - 'made with scrag end of neck, the bit of lamb that the butchers nowadays tend to give to dogs. But it was incredibly tasty and obviously you sucked the bones dry. Thursday would be usually breast of lamb, which was again very cheap. Fridays, it was always fish. Saturday might be belly of pork. And that was it, with only very minor variations.'

When food was at its scarcest, the priority was to make sure that George could earn a living. 'The idea that the kids get the best food in real working-class families isn't true. If the father was a manual worker, he had to have food so he could go out to work. So for tea on Saturday my dad would have - as regular as clockwork - a tin plate with cheese on it put under the grill. I still smell that cheese and think, "Oh God I'd love that."' But there wasn't enough money for the children to share in George's feast. Not that John or his brothers and sisters ever went hungry. To fill them up, Winifred gave them bread-and-butter pudding, made from stale bread from the bakery across the street, or 'we might have sugar sandwiches'.

What? 'Yeah, bread, bit of margarine on it and sprinkled with sugar.' I've never heard of such a thing, I say. 'Well you're bloody middle class, aren't you?' snaps Humphrys.

This poverty - and rationing - 'meant that everything had to be eaten and nothing was thrown away. I still can't throw food away. I'll eat food that is far past its sell-by date.' But, I say, you're a wealthy man now. Shouldn't you come to terms with the fact that you're well-off? Wasting food 'is a moral issue ... an immoral activity'. He repeats his point: 'immoral ... wrong ... absolutely wrong ... morally wrong ...' He avoids restaurants that serve up portions that are too large and always does his best to finish everything on his plate.

Clamping down on waste may be an obsession. Out of the corner of his eye, Humphrys catches sight of a group of diners sitting outside the restaurant. It is mid-October and they are being kept warm by a couple of huge gas-fired patio heaters.

'Look at those things outside ... Obscene! Grotesque!' he spits. 'Why can't they sit inside?'

After having listened to Humphrys for nearly 20 years on Today , I'm not able to let emphatic statements of opinion go unchecked. Why, I ask, shouldn't a restaurateur satisfy a free-market desire for people who want to dine al fresco?

Humphrys is having none of it. 'Does it ever occur to you what the world's going to be like when your son is 35 or 40, when you have grandchildren? Does that ever occur to you? So in 20 years' time when possibly his life and the lives of maybe billions of others is being made intolerable because of global warming - and this is no longer the realms of science fiction is it? - you'll say to him: "We had those patio heaters because it was nice sitting outside in the winter?"'

'Do you know how many patio heaters were sold at B&Q last year? And do you know what effect that is going to have, how much carbon dioxide is chucked into the air unnecessarily?'

So you'd have a law to stop us buying them? 'Oh I would ban patio heaters. Yes, absolutely.'

What else are you going to ban? 'Well that's a deliberately provocative and rather silly question. But if our elected representatives now regard global warming as the greatest threat to the world, the idea that they should ban nothing is a joke. You'll explain to your little boy in 15 years' time, "No, of course we didn't ban anything because we were liberals, we were libertarians ... and we wanted to enjoy ourselves ... Fuck you!"'

If I am taken aback it is not because Humphrys holds these opinions - though I'm a little surprised to picture a world in which we imprison B&Q patio-heater salesmen - but that he expends so much mental energy worrying about them. In the kitchen, for example, if he's making two cups of tea, he will carefully measure out two cups of water when filling the kettle. It's immoral not to.

'Doesn't everybody do that now? Yes they do. You may not. But why would you not? Why would you want to stand around waiting for two pints of water to boil when you want a cup? It's just idiotic! Stupid! It's a waste of time, it's a waste of water and it's a waste of electricity. So why would you do it? What point are you trying to make?'

He pauses, just long enough to put on a silly, mocking voice. '"Oh I'm rich ... Oh look at me, I can waste things, ooh, aren't I clever?" Well, bollocks! And it's no longer just irresponsible, it's morally wrong.' That word again. 'It's only people who've always been indulged in everything who don't give a bugger and now we're paying the price, aren't we? Now the middle classes are suddenly saying, "Oh yes, perhaps it's not a good idea."' Those pesky middle classes, again.

Humphrys does not, however, eschew all middle-class traits. He's just published an amusing book - his second on the subject - grumbling at the way language is misused, this time by corporations and official spokesmen.

He's also fond of noblesse oblige, and quietly donates thousands of pounds to good causes through the Kitchen Table Charities Trust, which he set up last year. The KTCT is an umbrella organisation that funds dozens of tiny Third-World charities that feed children and make sure they get to school, among other things. Humphrys raises the money by touring the country talking to rotary clubs, theatre audiences, anyone who'll pay good money to hear him. In its first year, the charity raised pounds 500,000. His target is pounds 10 million.

His other middle-class passion is, famously, for organic food. He briefly tried to make a go of running an organic farm a few years back - he made a lousy farmer, he says - and he is fiercely critical of the way supermarkets have, to his mind, promoted tasteless, junk food and put small local grocers out of business.

But, I say, his parents may well have appreciated the cheap food they sell. You can buy a battery chicken from Tesco for pounds 2.14. He's already told me that chicken was a luxury for his mother and father. Today, they'd be able to afford one every day of the week.

'Oh, those things. You call them chickens? I'm not sure they'd regard these pounds 2 chickens as chicken. They're rubbish, aren't they?' There's 'a moral price to be paid', because 'they're brought up in foul, disgusting conditions'.

'If you're asking me: "Is cheap food for poor people a good thing?" the answer is that it's better that they have that, yes. But equally - and it's not an argument that the bien pensants in their Hampstead homesteads particularly relish - the fact is that most people in this country today can afford to buy decent food. But if you choose to buy highly processed foods, it's more expensive.'

In any case, 'supermarket food is not very, very cheap'. Better, cheaper food - fresh meat and vegetables - is available in street markets and local shops. Almost uniquely in a country that is so reliant on food-store chains, Humphrys doesn't know the last time he visited a supermarket. 'I can't remember. It was years ago.' He implies that, for most of us, there's no need to use them at all.

Surely this is middle-class Humphrys shielding himself from the truth of life in some neighbourhoods, where a Tesco Express may be the only place to pick up fresh food?

Nonsense. 'Just over the way from here is one of the most unpleasant - or toughest, whatever you want to call it - estates in Britain, the White City estate. Have you looked at the shops there? I've been in them. There's a butcher's, where you can get bloody good meat, extremely cheap. There's a bakery, a grocer's and a chemist.' If such shops don't exist everywhere, as they once did, 'that's because Tesco has driven the buggers out'.

It's time the food industry was reined in a bit to enable poor people to eat better. He sighs. The state has got to 'lean much more heavily on the supermarkets. Salt content, for example. It's disgraceful we haven't forced them to do something about that. "Oh," ministers - of all parties - say. "Encouragement works best." Does it bollocks! Regulation works best: you order them to reduce the salt content of these foods by 50 per cent by next Thursday week ... The whole thing is scandalous, but we've allowed them to get away with it because, by and large, government is scared of the big supermarket chains and always has been.'

In any case, were they all forced to act together, none would be at a competitive disadvantage. 'And the patronising twaddle they talk about how people won't appreciate food without salt, that people won't eat it. Do the directors of the supermarkets lace their children's food with salt? I doubt it.' For his part, 'I never add salt to cooking. Absolutely never. If you want it, add it at the table.'

Humphrys is careful to aim his fire at 'government' - not this government - and ministers 'of all parties'. But even if this frank expression of views does not open him up to allegations of bias when he next interviews a member of the Cabinet, does he see a problem when Mr Tesco next pops up in the Today studio?

'I suspect Mr Tesco knows what I think about supermarkets. I don't regard it as a politically sensitive issue - nor do I deny that for an awful lot of people supermarkets have been a great boon. They certainly make shopping easier.'

I finish the wine - and notice that this time I am the one gulping it down. (Humphrys, quite rightly, has been doing most of the talking.) That's enough entertainment for one evening. This time, we agree, we'll give lap-dancing a miss.

· Beyond Words is published by Hodder & Stoughton (pounds 9.99). www.kitchentablecharities.org