A meal out for two on the continent costs just a few quid, yet here you're likely to end up with a £50-plus bill. Joanna Blythman investigates the UK restaurant trade and asks: are they ripping us off?

There are few pleasant surprises associated with opening a credit card statement, but eating out abroad is one of them. There it is in black and white - Restaurant I Bologna, in Rocchetta Tanaro, amount debited £63 sterling. I Bologna, remember, was that discreetly comfortable restaurant in restored stables in a small village not far from Asti, in Piedmont. The two of us ate courgette flowers in crisp batter with tender pink salami crudo di cascina; melon with lardo; wafer-thin vitello tonnato; a salad of warm quail and truffle; handmade tajarin (the Piedmontese version of tagliatelle) with pungent pesto Genovese; then had a choice of rabbit livers saut¿ed in balsamic vinegar or a giant porcini with poached egg on top; followed by local cheeses of impeccable provenance in peak condition; and even, unbelievably, found room for a toothsome semifreddo. We had felt like splashing out, so we'd gone for one of the best bottles from the cellar, Bricco dell'Uccellone, a sumptuous, somewhat rare barbera. The wine was expensive by Italian standards, £20 or so, but still not significantly more than it would have cost us in a local shop, while the eight-course food element worked out at a conveniently round £20 a head. How could such a feast cost so little?

Perhaps we should be asking instead why restaurants at home cost so much. There's nothing like a trip abroad to remind you how the eating-out pound buys you an awful lot more on the continent than it does at home, even allowing for the strength of sterling.

These days, walk into any vaguely aspiring UK restaurant that likes to think it has a chef in the kitchen, rather than a boy who reheats bought-in components, have a good if unexceptional three- course meal for two and an unremarkable bottle of wine, and you will easily walk out £80 the lighter. Head further upmarket, to an establishment that has more ambition, a better line in table linen, a more extensive wine list and lackeys who have been trained to chirp "Are you enjoying your meal?" at regular intervals, and you'll need to get your head around a bill that breaks through that psychologically significant £100 barrier and higher.

Maybe you're one of those people who pay up gladly without flinching, but many UK diners these days leave a restaurant feeling underwhelmed by the cooking and vaguely mutinous, suspicious even, about the bill. But do we really get such a bad deal? On the face of it, the British restaurant trade has a case to answer. The most obvious discrepancy is the mark-up restaurants routinely put on ingredients. Follow - as many chefs do - the latest food price watch in the industry's essential magazine, Caterer And Hotelkeeper, and you will note, for example, that "the price of farmed salmon continues to be at an all-time low". As a result, a chef can buy a one person-sized slice of fillet for no more than £1, yet a farmed salmon main course - with a few puy lentils alongside, perhaps, a blob of tapenade here and a hint of saffron in the mash - can sell for anything between £12 and £20. That's a breathtaking mark-up by any measure.

At one time, the profit margin on food - known as "gross margins" or GMs - to which the UK catering industry worked was 65%, but that is being nudged upwards. Nowadays, a chef is expected to make at least 70% profit on overall food costs. The typical rule of thumb for a mid-market restaurant is that if you buy the main protein element of a dish for £3, then you sell it for £10 and add another rounded-up £2 to make up for the 17.5% VAT that the government levies on your profit. All that takes the total cost of the dish to £12, which in the UK is considered a fairly reasonably priced main course.

But GMs are highly variable. A Gressingham duck leg destined, say, for a confit, will cost a chef about 60p, but it can go on the menu at upwards of £8 without anyone batting an eyelid. A plump duck breast of good provenance, on the other hand, might cost £4.50, which offers less of a profit opportunity to those restaurateurs with a more price-sensitive market.

Alternatively, there's the water at a fiver a bottle route. "The more cynical restaurateur might put on an attractively priced set menu at well below cost, knowing that he'll make it back on extras like cover charges, bread, water, wine, even fruit juice," says Chris Maillard, editor of Restaurant magazine. That's the formula for turning a £20 prix-fixe dinner into £40 a head in the blink of an eye.

Failing that, the vegetarian option is a particularly notorious licence to print money. Triple the cost of your ingredients, then add on a bit to allow for VAT, and your typical risotto, for example