If you've been more dazed and confused than usual ambling up and down the wine aisle at your local Tesco, blame it on Dan Jago and his accomplice, wine manager Jason Godley, because a warehouseload of their new wines has just hit the shelves. Godley claims that their new range makes it "the most diverse and exciting supermarket range in the UK". This could be taken with a large pinch of Maldon's, given the demise of Safeway and the apparent inertia at Asda, Somerfield and Morrisons. But as it still leaves Waitrose as the supermarket list to beat, a gauntlet of sorts has been thrown down.

You may not have heard of Dan Jago until now but he emerged as a first-time entrant to Decanter Magazine's 2007 Power List of Wine at number 12, ahead of such luminaries as Hugh Johnson, the EU Commissioner Mariann Fischer-Boel, Al Gore and, er, Richard and Judy. Why? Quite simply because "Dan the Man" was anointed head of drinks at the company with the UK's biggest share of the wine retail cake, at some 30 per cent. The usual platitudes about promising to increase the range of fine wines and reducing invidious promotions followed Jago's enthronement, but the proof of the drinking is in the bottle, so what better test than a preview of more than 100 wines from the 370 plus list?

The range doesn't just head upmarket with more than 200 of the new wines selling at £6.99 or more. It also introduces a raft of what Tesco calls "new and interesting grapes" such as Italy's Fiano, Falanghina and Arneis and Spain's Godello, Mencia and Verdejo. It expands the rosé section to 67, doubles the organic and fair-trade section, and, of greatest interest to serious wine drinkers, it has a stab at taking on board small parcels of high-quality wines, some of which, £10 plus rieslings for instance, are normally considered "hand sells" by sommeliers in restaurants because they need explaining.

In supermarket territory, you're never far from retailing jargon, and the latest theory that's caught the Tesco eye is the so-called Long Tail theory, espoused by the journalist Chris Anderson. Anderson's thesis boils down to the fact that in a retail world dominated by selling mass market volumes at low prices, it's becoming increasingly effective, especially with the availability of items on the internet, to sell smaller numbers of many different products – hence the long tail. Up to a point there's an element of "they-would-say-that-wouldn't-they?" when small parcels of wine can only go into selected top stores. But Tesco's website and the Tesco Wine Club, whose magazine reaches 525,000 homes, suggest that, managed well, selling small lots of premium wines will allow Tesco to access all areas.

For all the claims and jargon, Tesco has made a genuine effort to expand and improve its offering. The range of new sauvignons and chardonnays is impressive, among the former a capsicum and gooseberry rich 2006 Flagstone Free Run Sauvignon, £9.99 (204 stores), from the Cape, and rich, Graves-like 2006 Saurus Patagonia Select Sauvignon, £7.99 (71 stores). Among the latter, an oatmeal-scented and intensely peachy 2006 Errázuriz Wild Ferment Chardonnay, Casablanca, £9.99 (474 stores), is superb, along with a brilliant, classically proportioned, minerally 2005 Brocard Chablis 1er cru Quintessence, £14.99 (131 stores).

A section of exciting new rieslings includes the 2007 Spy Mountain Riesling, Marlborough, £8.99 (71 stores). There's plenty more to return to, and I haven't yet touched on the reds, but, as a foretaste, claret lovers might get hold of the fine 2003 Tronquoy Lalande, St-Estèphe, £12.99 (28 stores), a stylish modern expression of red Bordeaux with rich cassis fruitiness. The long tail looks set to wag for some time to come.