It was probably usually eaten cold, but by the 1830s, served hot, fried fish had become more broadly popular as street food.

Fish and chip shops began to appear in the 1860s, although there are competing stories as to the location of the first to be established.

These, predictably, are on opposing sides of Britain's north-south divide. The rival claimants are London - which asserts that the first 'chippie' was opened by one Joseph Malin in Cleveland Street in 1860 - and Mossley, near Oldham in Lancashire, which bases its claim on a market trader named John Lees, who started selling the combination there in 1863.

Neither date is definitive, but it seems likely that the chips migrated from the north of England, and the fish from the south, jointly colonising the whole of the British Isles.

Using vinegar as a condiment for fish dates back at least as far as 1845 when Eliza Acton published Modern Cookery For Private Families - the template for Isabella Beeton's later and more famous Book of Household Management.

By the 20th century, fish and chips was such a national institution that the ingredients were exempted from rationing restrictions during the second world war.

Nowadays in Britain, thanks to European Union directives, people know which fish can be found beneath the batter. But it has not always been specified, and different strains were preferred in different parts of the country.

The south of England must shoulder its share of the blame for cod's endangered species status. The north has traditionally preferred haddock.

Others widely available throughout the British Isles include halibut, plaice, sole, whiting, the misleadingly named 'rock salmon' - which is a species of small shark - and 'scampi', which is supposedly langoustine tail meat, deep fried in breadcrumbs, but which is often mixed with cheaper fish.

Few people in Britain visit a fish and chip shop without ordering chips, but not everybody likes fish, and most chippies today also offer sausages (battered or nude), pies, pasties and, increasingly, kebabs and pizzas. Pickled onions, gherkins and eggs can often be bought individually.

Mushy peas - a sort of paste jocularly referred to as 'the caviar of the north' - are part of the northern English gastronomic tradition, but are also widely available in the south.

In England, salt and vinegar are still the condiments of choice, although the American habit of using tomato ketchup is, lamentably, widespread. Brown sauce is popular in Scotland.

While chips may originate in Belgium, where mayonnaise is a de rigueur garnish, and Britain has a huge market for sandwiches soggy with the egg-oil emulsion, it has never caught on as a sauce for chips, except in the form of tartare sauce.

The availability of curry sauce in many fish and chip shops reflects the changing tastes of the times, and while there are people who think it goes well with chips, it is not to be recommended with fish, whichever species the batter may encase.

A degree of adaptability, as much as anything else, has ensured the fish and chip shop's survival. The institution was at its peak as long ago as the 1920s, when there were more than 35,000 of them in Britain.

The number today is only about a third of that, but choice has broadened, and for much of the British population fish and chips nevertheless remains the takeaway of choice.

It is not as cheap as it was, but in Britain nothing is, and the combination remains relatively inexpensive and - depending on the quality of your chippie - nutritious and delicious. Long may it last.