Our high street is a fragile but still functioning ecosystem - mainly because of the lack of predators

Or, at least it was until recently when Mr Clutch drove off into the sunset and was replaced by a Sainsbury's Local

(Ping Zhu)

Just up the hill from my flat is a main road. In truth it's a very main road, one of the first red routes to be so designated in north London. Cars and lorries and white vans and buses and 4x4s on the school run and motorbikes ridden by lunatics and funeral cortèges and coaches full of yawning tourists roar up and down it at every hour of the day and night.

We are shaded from its noise by some tall houses and the contours of the land, but the air quality can be challenging. Living on the main road, I've been told, is like smoking 20 fags a day. Admittedly I was told that by someone who does smoke 20 fags a day, which she may have momentarily forgotten. All that pollution can play havoc with your memory.

All the young couples walk past the Indians' shop and walk back 10 minutes later carrying orange bags

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While splendid for cars, the red route has not been unequivocally good news for the various retail outlets that line the road. In the quarter-century I have been living here, countless shops have been and gone. There was a wonderful DVD rental shop that had everything, except a business plan once downloading came in. There was a car repair shop called Mr Clutch, and we all used to wonder whether he was really called Mr Clutch, and had found himself running a car repair shop simply because he had been born with that name. Anyway, that's gone. For the longest time there was an Italian restaurant called Luigi's, whose menu never changed. We loved it. Only people with far too much interest in food could object to his huge and generously covered pizzas, and we soon learned to take those friends elsewhere. A year ago the restaurant closed for good, and a pall of gloom fell on the neighbourhood. Luigi had sold up and retired. To Italy? everyone asked. No, to Enfield, someone said.

All of which may sound slightly sad and doomed, like high streets everywhere, but the poor location can also work to these businesses' advantage. The chains have never shown any interest in our parade, and rents are modest, so people can open up the strangest businesses and prosper. The women-only motorcycle accessories shop is going great guns, while the menacing eastern European wine merchant has some interesting bargains you won't find in Oddbins. In short this is a fragile but still functioning ecosystem, mainly because of the lack of predators.

Or it was until recently. When Mr Clutch drove off into the sunset, he was replaced by a Sainsbury's Local, all bright neon and weary minions stacking frozen pizzas. At the top of my road is a neighbourhood shop run by a large and amiable Indian family, who have been here longer than I have. It's a great little place, and I often find myself going there three or four times a day for something or other. But since Sainsbury's came along, their turnover has halved, so that something that was flourishing is now barely viable. All the young couples who rent around here walk past the Indians' shop and walk back 10 minutes later carrying orange bags laden with stuff they could have bought for much the same price closer to home. Why? Because they want the Nectar points? Because there's a special offer on loo roll? Because it's brighter and cheerier and not quite so Indian?

Which only goes to show that if there aren't any predators where you are, it's only because they haven't found you yet. Tesco's are moving in now, apparently. So much for the fragile ecosystem, in this filthy north London air.

Illustration by Ping Zhu