Last month I wrote, a little indulgently, about my new orchard. It was a nice piece (he said modestly). Sweet. But not earth-shattering.

So this time I'd like to be a bit more hard-hitting and write something meaningful; something that actually makes a difference. I want it to be good, as in: if people read this, and understand my argument, and act upon it, then the net result will be undeniably good - either for them as individuals or for the planet generally. Ideally both.

To help me wake up a bit and think straight I've made a cup of tea - the drink that, in my experience, never lets you down (provided you make it correctly, but that's another story). It's Clipper Fairtrade tea, which I tend to alternate in my shopping with their organic tea. It's a moral each-way bet, like being Jewish one week and Catholic the next. I like Clipper because the tea is incredibly punchy and because it is a local company based in Beaminster, just a few miles away. OK, the tea is transported halfway across the world, but once packed it only has to travel a few miles before I can grab some. So I can say (in a way that I hope is more intended to stimulate debate than gain ethical brownie points by deceit) 'I even buy my tea locally!'

The milk in my tea today is Rachel's Organic. And I'm delighted to see that the packaging is delivering a deep-tissue moral massage. Not only is there a paragraph extolling the virtues of organic grazing and the superior omega-3 profiles of organic milk over conventional, there's also a big 'Help Give Cows to Africa' promotion going on. Wow! Rachel's pushing all my ethical buttons. In fact, if her massage wasn't so moral, I'd think she was practically a hooker.

Sorry, I didn't mean to sound cynical. I like these products. I think the organic and Fairtrade certifications are both meaningful and good, and I think you should buy them whenever possible. Why? Look, I know I said I wanted to make a difference this week. But forgive me if I can't quite face, in the limited space that remains, trying to grind out, one more time, a pithy and incisive summary of why I think these products deserve our support. It's just what I think, OK?

The fact is, when you're a professional foodie constantly trying to occupy the ethical high ground, it's hard not to feel a touch jaded. Especially when it starts affecting your kids. Recently Oscar, 7, has been conducting his own anti-McDonald's campaign in the classroom - and I didn't put him up to it. At first I was smugly pleased. But soon the strain began to show. Telling your classmates that their parents' most spoiling treat is an act of unforgivable wickedness isn't the best way to make friends. Last week Oscar came home from school exhausted and upset. 'Daddy,' he said, 'if McDonald's is so bad, why doesn't Tony Blair just make it illegal?' Why indeed.

While Oscar's campaigning zeal is wavering, Chloe, 9, has just made a breakthrough with fish. Until recently, she wouldn't touch it. Then I made some pollack fillets in crispy batter for the children's supper. She loved them. Breakthrough. Joy! So, on Sunday, we are all having lunch at the Harbour Inn in Lyme Regis. I'm ordering whitebait, trying to remember what Charles Clover has to say about it in The End of the Line, and worrying that, logically, eating about 50 infant fish at a single sitting can't really be a good thing. Chloe wants cod in batter. Oscar gets excited: 'No, Chloe, you can't! Cod's endangered! We're not supposed to eat it!' Chloe, who was feeling proud of what she thought was a brave and parent-pleasing choice, has tears welling in her eyes. I rule in favour of Chloe getting her cod. Oscar musters a devastating look that accuses me of weakness and betrayal and, worst of all, predictable adult hypocrisy.

Meanwhile a friend (grown up) whom I greatly admire is spearheading the lobby that is currently trying to persuade the meat buyers of all the major supermarkets to insist that their meat is all reared on GM-free feeds. But it looks right now as if they will fail. Because, according to the biggest supermarkets, 'there is no consumer pressure on this issue ... our customers don't want GM in their tomato sauce, they've told us that, but they don't even perceive it as a problem in meat...it's just not on the radar for us ...' (my paraphrasing, of course). How depressing is that?

Actually, strangely, not quite as depressing as it might at first seem. If, like me, you are struggling to pick a clean path through the moral maze of the average food shopping trip, and wondering whether your choices (and indeed columns like this) can ever really make a difference, then take heart from the amoral cynicism of the mega-corporations of industrial food and agriculture. Say and do nothing and you are off their radar. But make your feelings known, however messily, lazily, and inconsistently, and it seems you might just be heard. The process of engaging your conscience with the food market place may be agonisingly slow, utterly exasperating, borderline soul-destroying ... but it is not entirely without hope.