FOR many people, not a few of them British, the idea of returning unacceptable restaurant fare to the kitchen or cellar is unthinkable. The very fact that they are being served in a restaurant is supposed to be a guarantee, and when it is not . . . well, we all fail sometimes, don't we?

At the opposite end of the scale, some Americans of my acquaintance, who fancy themselves as connoisseurs, enter restaurants in the way a minesweeper enters infested waters: with a determination not to get caught out, be imposed upon, cheated or in any way not get their money's worth.

Most of us fit somewhere between the two extremes: loath to send something nasty back, but sometimes obliged to do so; ever polite, and inured to the fact that restaurant dishes are seldom as good as they are made out to be.

On the whole, wine is easier to handle than food. There are certain standards to go by, and one can be sure that most sommeliers know little more about the wines they serve than do their customers.

In fact, the longer and more pretentious the wine list - and the more obsequious the sommelier - the less likely he or she is to have drunk the wines served, especially at the pricier end of the range. Few, indeed, are the restaurant owners whose sommeliers pick the wine and are allowed to indulge themselves in the odd bottle at the owner's expense.

Nevertheless, sending wine back is a fairly straightforward procedure. It is easiest when it is clearly bad or over the top: the dumbest wine waiter knows the sickly sweet smell of a bottle that has had its day. In my time, I have sent back premiers grands crus at Claridges with nothing more than a reproachful look and a mild argument from the sommelier.

Harder to send back is the bottle that is not as represented: it is the wrong year or the wrong vineyard, and you have not noticed this fact until your guests have been served. But the technique is the same: be firm, offer to let the sommelier see and taste for himself, make a modest apology and, if necessary, insist on your rights.

Few waiters, however, will have a fork handy with which to seek to pierce that impenetrable cauliflower stalk, or would venture to taste a bad oyster, or sample a piece of fish that has not been cooked at all in the middle. Here the technique, adapted from that of my mother, a dragon, is more forthright: one simply puts knife and fork together, summons the waiter and says: 'This is inedible.'

You have certain rights, legal as well as commercial. You are neither obliged to eat nor to pay for unsatisfactory food. A dish returned is not one that will come back in court to haunt you. If, as I recently described, a steak au roquefort turns out to contain no visible or tastable roquefort, you may say: 'This is not what I ordered.' If told that the kitchen is out of roquefort, you may make a scene and order something else. As the friend of many restaurant cooks and owners, however, I suggest a dose of fatalism and a touch of charity. The smart owner - not the one in whose restaurant I ate that steak, for he fancied himself and offered only a mild apology after continued protest - will simply not charge you for the dish.

The most frequent objection to meat is that it is not cooked as specified, and here the customer has to be wary, for national characteristics have much to do with the definition of 'rare'. Saignant in France is bloody rare in Britain; a point is more frequently medium rare. In Spain and Italy, save for the best places, the words do not exist and you will get meat the way their nationals want it: overcooked.

My chief difficulty with steaks is that if you get one which is underdone, the restaurant may well throw it back on the grill, and the inevitable result is that it comes back to you overcooked. What do you do if it arrives overcooked? Most of us do not like waste and hate to throw a perfectly good piece of meat away just because the cook was asleep at the switch.

This particular problem seems to me insoluble. I eat it: not out of cowardice, for I never fail to remark on the cook's failing, but because I would rather not raise my blood pressure and risk the cook's ire for the rest of the evening.

Bad service can always be reflected in the tip. Where it is included in the price of the meal, you may refuse to pay the service charge. I do not say it is easy; I just say you may try it. I have had marathon arguments in so doing, one involving the police. Luckily, the policeman in question was French, understood food, and allowed that I was right: the waiter was untrained, rude, got two dishes wrong, then served the wrong dishes to the wrong people, and generally treated us as if we were dirt. The owner defended him stoutly, but in this case to no avail.

On the whole, however, remember that cooks are fallible; that romance is ever- present in the designations of dishes; that in the absence of X, Y may be used and the dish may be no worse. It is better to err on the side of charity than arrogance, but that is positively no excuse for remaining silent. For how can a restaurateur improve his establishment if he is not told when he makes serious mistakes? My mother could do it with a look. I, alas, must use words.