For the new 2010 edition of my annual guide, The Best Wines in the Supermarkets, published this week, I have tried more than 2,500 of the wines sold by 10 of the leading chains. Of these, 500 have made it into the book as recommendations.

On the rounds of the tastings staged by the chains this year, talking to the clever people who source the wines, the theme has been, obviously enough, value for money.

Customers are cutting down on what they spend on wine and looking more eagerly than ever for bargains and the supermarkets are working very hard to oblige them.

Several of the chains – including Waitrose – made their cheaper wines a special feature of the tastings held in 2009, and I was consistently impressed with the quality, even at the lowest prices.

It's only fair to point out that more than half of what you pay per bottle goes in tax. It works like this: every 75cl bottle of still wine incurs excise duty of £1.61. So, if the retailer pays, say, £1 for the wine, £2.61 is handed over to the supplier, plus 15 per cent VAT on the lot (yes, excise duty is vatable), making the total exactly £3. Retail mark-up is normally 30 per cent, and that's how the £3.99 price on shelf is arrived at. In short, a £4 bottle of wine is really a £1 bottle of wine.

How the producer of the wine can make a profit out of £1 a bottle, which has to cover the cost of growing the grapes and vinifying them, bottling and dressing the finished product and shipping it sometimes enormous distances to Britain, flummoxes me entirely.

There are just over 50 sub-£4 wines recommended in the book, more than a handful at £3.49 or below, including a very appealing dry white from Asda, Marsanne Vin de Pays d'Oc 2008 at £3.28, with "a distinctive almondy-apricot richness balancing the keen crispness of flavour" and from Tesco, Siciliano Rosso 2008 at £3.23, which I describe as a "fantastic island red that brings sweet herbaceous character to redcurrant and cherry fruit... unbelievably cheap".

Whether these prices can be maintained is another story. The pound is down to near its historic low against the euro, and there are gloomy predictions that some time next year the two currencies could be on a par. And while sterling has held up a bit better against the dollar and southern hemisphere currencies, it's still a long way down on the levels of 2007-08.

The cost of imports (and 99.9 per cent of our wines are imports) from the EU must rise sharply in the near future, and from the New World likewise, if more modestly. To cap it all, the VAT rate is due to return from its temporary 15 per cent to 17.5 in the new year – or, if the doomsayers have it right, to something higher.

Right now, you might expect that the cheapest wines are proving the most popular. But according to a survey by the Wine and Spirit Trade Association, this end of the market is being squeezed hard. Sales of bottles costing under £4 have fallen 11 per cent between 2008 and 2009, with many people on lower budgets simply being forced out of wines completely.

We should, of course, think of the problems faced by winemakers worldwide who depend largely on our custom. But we do have troubles of our own in the grip of this terrible downturn, and surely deserve a decent glass of wine to cheer ourselves up.

The Best Wines in the Supermarkets 2010 is published by Foulsham priced £7.99