What happens next is up to you. You must decide whether to complain, and how far to take it. A mild query? A bold refusal to drink or pay? As we supposedly become a nation of restaurant-sophisticates, the question of complaining about wine remains as thorny as ever.
Not that wine writer and television presenter Alice King and her husband Nick Davies had any doubts about what to do. Yesterday, it emerged that Miss King, author of the Hamlyn Atlas of Wine, has been banned from a restaurant in Marlborough, Wiltshire, after she complained and would not pay for a pounds 16 bottle of Beaujolais, because it "lacked fruit and tasted dried out".
They stood their ground, and at one point the row became so heated that other customers, who were asked their opinion of the wine by the manager, backed the restaurant and urged the King party to pay up. Another diner, who liked the wine, even chased Miss King and her party down the street, hurling abuse.
So, how can such a dispute be settled? The law on wine (and food) in restaurants is quite clear, being governed by the Trade Description Act (1968) and Sale of Goods Act (1979), among other acts of Parliament. The goods must be of satisfactory quality, fit for the purpose and as described on the menu. But problems abound despite that apparent simplicity. Customer says: "my wine tastes like something poured from a fish tank." Waiter says: "this wine is delicious." Who's right?
There is one clear case in which wine may be returned: when it's "corked", tainted by a fungus that occurs naturally in some cork trees. Corked wine is akin to rancid butter or shoes with a hole in the toe - clearly unfit for use. It's worth noting, however, that I've watched people drink corked wine and not notice the fact.
The problems are trickier when the wine is alleged merely to be not as good as it should be, as in the case of Miss King, or when customers order the wrong bottle out of sheer ignorance - "We didn't know Cava has bubble" - or when they simply decide that they don't like it. When it's a simple question of not liking the stuff, the law would be on the restaurant's side.
But the restaurateurs I talked to were unanimous in proclaiming a generous attitude, even when the customer is wrong. Georgina Thompson, of London restaurant 755, says they get a complaint once every couple of months. "If there's a genuine fault with the bottle," she points out, "we can always send it back to the supplier. And if there isn't anything wrong with it, it's better to have a satisfied customer than one who is not. Satisfied customers come back."
Michael Gottlieb, proprietor of the Smollensky restaurants and Cafe Spice Namaste in London, agrees with that point of view. "It doesn't happen often, but when people complain about a bottle we replace it without question. And sometimes give a couple of glasses of free dessert wine just to make sure they are happy. Our first priority is to look after customer."
That is also the view of Barry Phillips, of the White Horse in Chilgrove, West Sussex. His list, one of the most extensive in the country, includes dozens of bottles of great rarity and antiquity. So he does have to contend with complaints about expensive wines - and they seem to be delivered in the nicest possible way.
"We had to take back three bottles of La Tache '71", he recalls. "I think it cost pounds 300 the last time we sold it. One bottle was out of condition, yet the customer insisted on paying part of the price. Another bottle was bought by someone who tasted it and said, 'I don't mind paying, but do I have to drink it?'"
Friendly customers make it easy to be gracious, but despite the higher sums at stake, the White Horse policy mirrors Gottlieb's. "We want people to be happy and comfortable. Someone sent back a magnum of Krug '79 [around pounds 350] because he thought it was flat, and we accepted it."
I hope you never find yourself in Alice King's position. But if you do, there are four points to bear in mind. First, you have to decide how much palaver you are going to tolerate in making your complaint. Some people, faced with a waiter who refused to take back a bottle, would give up - or just deduct the service charge, which is their legal right.
Second, in making your complaint, deliver it quietly and without pretence. "Waiters hate customers who show off," says one hard-bitten veteran. Third, if you think the wine is in that legal grey area - not really spoiled, but not nice to drink - make it clear that you understand this is a matter of opinion. And if it's a perfectly good bottle but just not to your taste, throw yourself on the waiter's mercy.
The fourth point arises only when fisticuffs are threatened: when the restaurant won't back down, and neither will you. As Gottlieb says: "If you are a customer and you believe you are right, stick to your guns. Tell the restaurateur: 'It's my right not to pay for wine I think is faulty, I am not going to pay, and I'll see you in court.'"
That approach will not make your evening a relaxed one but it will make it interesting.
Richard Erlich is drink writer on 'The Independent on Sunday' and recently won the Glenfiddich award for drink writer of the year.
britain's favourite tipple
Two thirds of the adult population of Britain drink wine - more than twice as many drinkers of any other alcoholic drink.
The British spend pounds 5.85bn on wine each year, pounds 2.82bn of which is spent while dining out.
Around 678m litres of wine were sold in Britain in 1996 - a rise of 16 per cent since 1992.
Red and rose wines have overtaken whites in popularity, with their sales expanding by 55 per cent since1992. By the year 2001, they will account for 55 per cent of the market.
German white wine remains the single most popular choice - Portuguese is least popular.
British wines account for only 4.2 per cent of sales.
The biggest drinkers of wine are aged between 35 and 44 years old.
The wine market is forecast to rise by 25 per cent by the year 2001.
Around 9.8m cases of wine are imported from France each year, a result of their negligible duty on alcohol.
Only 6.6 per cent of the wine-drinking public choose non-alcoholic varieties.