Blah, blur, ahh. Ahem. Sorry about that. Mouth a bit dry. Hands typing this are weirdly disconnected from the brain. But, when not putting CAPS LOCK on by accident, I want to tell you what happens when you order four glasses of wine over lunchtime. In the traditional scheme of things this would be a modest four units. Four small glasses of, say, a light German Riesling, comfortably meets the amount a man can drink in one day on his way to the government's recommended limit of 28 units a week. But now the world of wine has gone extra large. These days four glasses of wine at lunch can equal quatre monster tumblers bearing in excess of 250ml each. Add that to today's increased alchohol levels - 14% wine is no longer seen as strong - and, four glasses later, you could have downed a colossal 14 units. That's the weekly recommended maximum for a woman, according to the British Heart Foundation, and all in one lunch hour.

Director of addiction services to the stars, Nick Gully of the Priory Clinic in Roehampton, has this week issued the latest in a series of warnings about the growing size of wine glasses. The extra-large glasses we are now routinely handed in pubs, bars and restaurants is creating a nation of "unwitting" alcoholics, according to Gully. The ordinary drinker, he says, has learned to feel cheated if she or he goes into a pub and is served up the once standard 125ml thimble of chardonnay. Punters have developed a physical and psychological (try spelling that after four extra-large glasses of sauvignon blanc) dependency on extra-large helpings of booze - and have learned that drowning themselves in wine is entirely acceptable.

This is Super-Size Me for the chardonnay-quaffing classes. But is he right? Are we really becoming a nation of accidental drunks? Or are we savvy enough to work out for ourselves how much we're drinking, even if the glasses are getting bigger? As the saying goes, it's a tough job but ...

I begin in the Apple Tree in north London at 15 minutes past wine'o'clock on a Monday afternoon, with an empty stomach and no particular thirst for the devil. Could I have a glass of white wine please? "Chardonnay or sauvignon blanc?" says the barman. "... large?" The way he says it leaves little choice. The common-sense choice is clearly large. And for a while, it is. Chilled sauvignon blanc at 11.5% slips down rather more easily than I expected at a loss to my wallet of £4.40.

"I always ask large or small but we serve more people with large glasses," says the barman. "It looks nicer, swilling around in a large goblet-type thing." He argues that drinkers actually relax and take it easier holding a veritable vat of wine. "People drink more when they have a small glass. You don't swig a large glass like a pint."

Four swigs later, I'm leaving the Apple Tree. Over at the Red Lion, punter Chris Williams is a firm believer in the healing power of an oversized vessel of plonk: "I drink wine when I'm detoxing, because it's got fruit in it." Williams, a barber who swears by the steadying hand of a lunchtime draught, says he has proper wine glasses at home: they hold half a bottle each. "I drink large glasses of wine because it saves me asking at the bar for a drink so often. In this pub they are known as goldfish bowls." Halfway into my second glass, there is a noticeable two-second beat between my brain instructing my hand to raise the goldfish bowl and it appearing in my hand. Pork scratchings. Yum.

I am unfit to drive anywhere but, in my hazy theory, I have had just over one unit of alcohol. "People are aware that glasses are bigger and wine is more alcoholic but no one seems to be aware that the idea that a glass of wine equates to a single unit is completely out-of-date," says Victoria Moore, a wine critic for this paper. One unit, she points out, would be a 125ml glass of 8% dry German Riesling, which no one drinks any more. Most new world wines clock 14%. A large bar measure is three-and-a-half units in one glass.

"The whole heinous thing about it is wine is really revolting served in a big glass," says Moore. "It gets warm so fast, it's disgusting. By the time you get halfway down, your glass is all smeary."

Moore is firmly in favour of less. "People always look at me a bit funny when I give them a puddle of wine in the bottom of the glass. In restaurants you think it is good service when they refill your glass from the bottle, but they will fill your wine to the brim and it gets through the bottle really fast. I'm always shouting at waiters in restaurants, saying I only want my glass filled halfway."

Shouting at waiters. Hmmm. One in five young men has ended up in a police cell after drinking to excess, according to a recent study funded by the drinks industry. The Drinkaware Trust found that a third of young men said they felt "aggressive" after downing large quantities of alcohol, a figure that rose to almost half in London. This statistic comes to mind after my third large glass in the Bleeding Heart, a glassy, er, classy, French bistro-style bar.

According to Moore, continental drinkers are not seduced by 250ml culture. "If you go to France or Italy or Spain they either serve those delightful little beakers or they will never pour your glass more than half-full - it's considered vulgar." The view from Britain is somewhat different: "When we went to Paris and ordered a glass of wine it was like a thimble," says Jason Elder, a punter. "I don't think people are complaining about the measures here."

The Bleeding Heart is about as continental as it gets in our capital. "I like to think that wine by the glass comes in small, medium and serieux," says one businessman. "It's up to the individual to decide whether they want a large glass or not," says Tom Jansz. "There's all this thing at the moment about McDonald's but it is people's responsibility to look after their health. You don't have to buy them. I don't like the small glasses of wine but it's more of an aesthetic thing than anything." But aesthetics exert a powerful social pressure when it comes to buying drinks. As Elder points out: "You go to the bar and they say 'Small or large?' and you don't want to seem mean or cheap so you get the large."

Three glasses in, however, and the world takes a perplexing turn. Not content with supplying me with a white wine somewhat smaller than the red tulip-style glasses being knocked back by the businessmen, the French waiter takes exception to presence. "Can you stop disturbing my customers, pay your bill and go please," he says, in a magnificently snotty tone.

I saunter, slightly tearily, to the Crown, a pub offering 15 types of white wine and 16 of red. I am served up a large glass of Soft Banks from New Zealand, kicking in at 13%. The barmaid reckons two-thirds of her customers plump for the small option at lunchtime, but this statistic is reversed in the evenings.

It is a trend picked up on by Patrick Barker (no relation). "When I was your age we'd have a bottle of Bull's Blood and a bottle of port and go back to the office and write a report," he says, sharing a bottle of red with his drinking companion. Barker does not consume wine by the glass. "I think young people drink a hell of a lot more but they don't drink at lunchtimes. When they go out of an evening, Christ. I'm nearly 60 but when I was a kid the only alcohol in our house was some cherry brandy or sherry left over from Christmas. There was no question of wine with your meal. Drinking has increased because the opportunities for drinking for longer have increased."

That may well be true, but four glasses in, albeit three unfinished, I am no longer in a position to judge. Time to head back to the office for a snooze. Cheers.