A little while ago, a senior editor on this newspaper invited me to lunch. 'And bring a ruler,' he said. 'We're going to Pizza Express.' My boss reckoned he had spotted a story: the pizzas at Pizza Express were, he said, getting smaller. So we sat in a north London branch and when our pizzas arrived we measured them. They were exactly nine inches, as they have always been. To be fair, he was hardly the first male to have a problem estimating nine inches by eye alone, but I think his nose for a story was absolutely spot on - if Pizza Express had been trying to subtly reduce the size of its product, an enormous slab of the British middle classes would have risen up in revolt.
Pizza Express occupies a very particular place in the affections of the British: it is a fast-food joint that is not too fast, a reliable dispensary of food sprightly enough to appeal to children and sophisticated enough to appeal to their parents who, eating there, can again feel like adults. A few years ago, after a period of expansion through franchising, the parent company recognised that standards were slipping and bought back all but three of its branches. The good management of its brand requires simply that nothing must change. Well, almost nothing. Because, for the first time in more than a decade, the company has had a rush of blood to the head. It has introduced four new pizzas.
I visited the branch in Tunbridge Wells, a branch much like any other of the 240 odd in Britain: cool white walls, potted palms, a smattering of tasteful modern art, light jazz on the stereo. And so, too, the lunchtime clientele. Here, a table of mothers with their collected brood; over there, grandparents spoiling the next generation; by one window, a works lunch; by another, a single woman finishing a bottle of sparkling mineral water. Witness, then, the middle classes at rest.
Of the four new pizzas, I chose the one I would be least likely normally to order: the Caprina, with sun-dried tomatoes and goat's cheese, at £5.90. The goat's cheese was salty and rich, and the chopped sun-dried tomatoes were pleasingly soft. As for the base, it was, as ever, that careful balance between chewy and crispy. There's a sensible list of Italian wines from about a tenner to £14 but, this being a lunchtime, I was not in the mood for wine. I had a Coke and a side salad, and the bill came to a little over £10, including service. You can't really gripe, can you?
A little later, I tried the other three pizzas from a newish branch in Kennington, south London. The one guaranteed to find a particular audience among 10-year-old boys is the Sloppy Giuseppe, £5.95, a pretty brutal combination of spiced beef, green peppers, chilli and cayenne which, if it were not for the base, would be more at home at Pizza Hut. It's a crude flavour kick.
The Soho Pizza, at the same price, is testament to just how successful the food revolution has been in Britain, depending as it does on a good handful of fresh rocket to cover the topping of Parmesan, olives, garlic and mozzarella. The result is a subtle pizza, the softness of the peppery rocket working well against the bite of the olives. But for me, the winner is the Pizza alle Noci, £5.85, an unctuous assembly of walnuts, lemon zest and gorgonzola.
So change is abroad, in a place where the clientele least like it. But the middle classes should rest easy. It's a very British kind of change: gentle, with a bit of tinkering round the edges.
• Pizza Express, 81 the High Street, Tunbridge Wells (01892 543 112), and in 240 other locations all over Britain. Meal for two, including wine and service, costs around £30. Jay Rayner can be contacted at jay.rayner@observer.co.uk
