'I'VE loved them for years. They are not too sweet or full of disgusting goo,' says Simon, 34, an insurance broker. 'They are simple and elegant. A Mars is too voluptuous, a Twix is just too icky.'

Kit Kat has a special appeal for the more mature snacker.

'They are my favourites - they are not a childrens' chocolate, they're a big boy's bar,' says comedian James Whale, who thinks he could eat 'probably half a dozen' at once.

They can be eaten anywhere without embarrassment.

'It's a very clean bite, you don't get a load of sticky strings hanging out of your mouth,' according to Nick, 28, a writer.

Kit Kat - which will be 59 this year, and has barely changed composition or wrappings for decades - has easily beaten new-fangled Twirls, Chomps, Strollers and Fizzy Chewits to become Britain's top-selling sweet for the seventh year running. The name was registered by Rowntree in 1911, 'probably inspired by London's sophisticated Kit-Kat Club, though the origins of the name are lost in the mists of time,' says Hilary Parsons, of Nestle Rowntree.

The product, with its excitingly modern and innovative wafer fingers, was finally launched in 1935 as Rowntree's Chocolate Crisp and became Kit Kat Chocolate Crisp in 1937 - advertised as 'a two- course meal for 2d' with a luxurious 'lacing of the finest butter', in the familiar red wrapper.

Kit Kat even did its bit for the war effort: no milk was available so it reappeared in an austere plain chocolate guise, packaged in blue. Advertisements stressed that those keeping the country going could work for two whole hours on a single block; and warned eager but frustrated buyers 'if Chocolate Crisp is out of stock, don't blame the shopkeeper. He does his best to get it and we do our best to keep a fair supply all over the country.'

Today's Kit Kat costs 23p for a four-finger bar. Last year's UK sales of pounds 210m were were pounds 60m ahead of Mars, the number two seller. Holidaymakers need not worry about Kit Kat deprivation - it is available in 13 European countries (number one seller in Spain and Portugal - and Saudi Arabia, where it lives in the fridge), as well as Canada, South Africa, the US, Malaysia and Japan. Forty seven Kit Kats are eaten every second.

Why is it so popular? Partly the nostalgia factor, but American psychologists have also identified a backlash against healthy eating, the 'pleasure revenge', as burnt-out, starving grown-ups reject exercise and tofu in favour of slobbing out and chocolate.

The Action and Information on Sugars group of nutritionists, dentists and child health specialists leapt to condemn the 'aggressive advertising' that encouraged the consumption of a record pounds 4.4bn worth of sweets last year. The 'Have a break . . . ' ads are recognised by 99 per cent of the population.

But a group of schoolgirls in a south London sweetshop had failed absorb the message. 'Kit Kat is boring. My mum puts it in my lunchbox but I swop it with friends,' said Amber, aged 15, disdainfully. 'We like Twix, because it comes in different flavours now.'

Chantal Coady, co-founder of the Chocolate Society, is equally unimpressed. 'Kit Kat's success is down to a craving for sugar and comfort food. English food is getting more sophisticated, but the English still have very unsophisticated palates.'

Not all Kit Kat fans are just chocoholics, though. 'To eat, I like Bar Noir or Fruit and Nut,' said Susan, a housewife. 'What I really like about Kit Kat is that trick-cyclist panda ad.'

A polite lack of enthusiasm was the reaction of Tom, 14, who observed condescendingly, 'It's quite crispy, which is nice, I suppose.' But, he pointed out, 'once you've eaten one Kit Kat you've eaten them all.'

(Photograph omitted)