I check into The Sampler in Islington's Upper Street, where Dawn Mannis thrusts a smart card into one hand and a glass into my other. I slot it into a stainless steel, glass-fronted cabinet holding eight bottles, press the button above the sign reading Sancerre, and hey presto! It obligingly dispenses a 25cl serving, deliciously chilled. I try the Pouilly Fumé beside it, moving on to the next dispenser for a white burgundy and a New World chardonnay. Just as well I'm spitting. Next stop the 2004 Ata Rangi Pinot Noir, a Charmes Chambertin, then on to Spanish and Italian. For my £20, I feel as though I've tasted half the world, but I still seem to have enough credit to visit the icons machine where I taste a graceful 1959 Beychevelle, a youthful 1999 DRC Romaneé St Vivant and a grand 1995 Château Latour.

Dawn and her partner Jamie Hutchinson had long wanted to run their own wine shop, but it was only when they came across the Enomatic at a chianti tasting in Tuscany three years ago that they hit on the idea of making the sampling machine the focus. "Lots of people can't afford expensive wines," says Dawn, "but this system allows them to try before they buy." Basically, each Enomatic (they have 10) holds eight bottles, keeping the wine fresh for up to three weeks. Not that any bottle actually stays that long unfinished. When they opened for business in December, the custom was mostly locals coming in to buy wine, but now people are coming in as much for the tasting experience itself.

In addition to the 800-plus wines on the shelf, 80 wines are available for tasting at any one time. Each wine has its own tasting note. "It's like painting the Forth Bridge," says Dawn, enigmatically, but you get her drift when you see how much work goes into it. You can compare your notes with theirs. Four machines hold white wines, six reds, and each machine is based on different styles and grape varieties. "Bordeaux in the £17-£30 range is our bestseller," says Dawn, "but Spain, Italy and white burgundy do well too." The single bestseller is the sumptuous Wild Earth Pinot Noir from New Zealand. Samples range from 30p to £30 for the 1999 Pétrus, which disappeared surprisingly quickly.

There must be something about Pétrus – and Dawns for that matter – because when I arrive at Selfridges shortly after, there was another Dawn to show me around their revamped wine shop and Wonder Bar. There, at the table next to ours, was a group guzzling, or sampling should I say, a 1996 Château Pétrus. This new Dawn, Dawn Davies, heads up Selfridges' answer to The Sampler, created by the food and beverage manager Ewan Venters. Like The Sampler, the main feature of the new Wonder Bar is also the Enomatic machine, which Venters likens to a jukebox. After stumbling across the idea in Tokyo, he decided it would be perfect for Selfridges, enabling customers to enjoy the try-before-you-buy-experience or sample Dawn's eclectic choice of wine, with food at the bar.

I try a 2005 Chapel Down Bacchus, a 1989 Pichon Longueville, yes, and that 1996 Pétrus. With a seafood platter, I have a sip of three unusual dry whites: a refreshingly peppery 2006 Angerer Grüner Veltliner, a characterful 2005 Jermann Pinot Grigio and a peachy 2006 Pinot Heartland Gris / Viognier. I try a red saké, whose existence until that moment I had no idea of. Now I'm getting the hang of this. A few days after my visit, along comes a jobsworth from Westminster City Council to rain on Selfridges' parade. Yes, you can have a 125ml or a 175ml glass, he says, because the 1988 Weights and Measures (Intoxicating Liquor) Order decrees it. No, you can't have a 25ml or 50ml serve, he says, because the Intoxicating Liquor Order doesn't allow you to take a smaller sipping sample with your food. Who was it who said the law is an ass?