They're round and a bit boring. So why is everybody wearing them? Helen Fielding reports
"OH, LOOK AT these. Oh, these are fantastic. Oh, these rurely are superb." What was extraordinary about this enraptured outburst from a smart middle-aged woman was that a) the source of her joy and marvelling astonishment was a pair of National Health-style spectacles, and b) they seemed to be exactly the same as almost all theother pairs in the shop.

People love these glasses - roundish, with wire rims coated in horn-style plastic - they love them. On one recent Tube journey from Tower Hill to Bank, every single spectacle-user in my carriage (seven in all) was wearing them. Not only that, but the world's largest spectacle manufacturer, Luxottica, say that nearly a third of the glasses they currently sell in Britain are based on this look.

Brian Keefe, director of the optician chain Dollond and Aitchison, claims they account for nearly 90 per cent of their sales in London's West End and a quarter in Britain overall. They sell them to tiny infants, young people, middle-aged people, men, women, working people, professionals, celebrities. Why should a small, unprepossessing spectacle capture the Zeitgeist in this outlandish way?

The retro glasses first started to re-appear about five years ago, championed by Giorgio Armani - still a market leader with the frames - giving a serious, intellectual dimension to handsome and affluent-looking models. The look was taken up by a rash ofAmerican celebrities: Sylvester Stallone, Kevin Costner, Michael J Fox. Spectacle designers began to churn out a plethora of variations. The frames (called PROs, Panto Round Ovals) echo a utilitarian National Health style - number C223 - which was available from 1948 until 1986 when the National Health frames were scrapped. "People used to really hate them," said Brian Keefe, "It's very odd." John Dinning, marketing director at Luxottica laughed: "I wish I could explain the appeal for you, but I can't. I really can't."

There have, as Dinning explains, been pronounced spectacle trends before. In the Fifties and early Sixties, when non-utilitarian design took off, glasses with wings were very much the thing for women: wings on top and clear frame or no frame underneath. For men, the wings were muted into black flashes. In the Sixties, the John Lennon-inspired small, round, wire frame took hold - harking back to the Twenties and Thirties - titillated into various fashion versions: silver, gold, spherical, even hexagonal.In the late Seventies, big plastic glasses took over, wackily hued, Christopher Biggins-style.

But until the PRO, as Dinning says, "The trends which got talked about were really a question of niche marketing: appealing to young or metropolitan people. This level of market saturation is very good for us, but it isn't normal."

Could anxiety about the ailing National Health service be the key? Shame at not having appreciated what we once had? A desire to make amends now and express solidarity or support? The national subconscious throwing the glasses up onto the nation's noses, like yellow ribbons for John McCarthy or red ones for AIDS awareness?

"Oh no, it's nothing to do with the National Health," Jane Parrot, a glamorous 24-year-old secretary, sporting the frames, told me when accosted in the street. "This is what I like," she said, pointing to the Giorgio Armani inscription. "When I went intothe shop I didn't go in with the intention of buying any other shape. I mean, you look round on the Tube and everyone is wearing the same ones. I don't know why I like them. It's weird."

It is. A 27-year-old supermarket buyer from Yorkshire had rather opposite instincts: "I almost didn't buy them because of the Giorgio Armani logo. In fact, I was considering scratching it off. It's back to basics."

But the lady who had been enthusing rapturously in the spectacles shop, a 47-year-old art historian from Kilkenny, said she felt the glasses represented "a kind of old-fashioned socialism. I think they suit me. I want to look business-like and professional without looking schoolmarmy." And yet for others, the brainy look is precisely the appeal. "They do make you look bookish, I like that," said Simon Perry, 28, chisel-jawed and worthy of an Armani poster. "But I don't know, I just like them. My brother's got a pair, and so has my girlfriend's brother."

But the tide is on the turn. Already there is talk of things to come in the form of tiny ovals, or an upswept cats-eyes look in thin, muted metals. What the PROs seem to have captured is the shifting, ambivalent mood of the moment: a hint of socialism, with monetarist price tags; an air of bookishness and depth combined with stylish affluence, a classless man-of-the-people look with a designer label; understated, yet grungily self-aware; looking forward yet, er, backwards at the same time.

They are a spin doctor's dream. What are the Cabinet doing in their square or oblong frames in unbroken dark plastic? How can they hope to succeed? Major, Hurd and Howard must change their eyewear swiftly, before the moment passes and they find themselves having to keep up by wearing cute little up-swept cats-eyes, possibly with wings on.