a car wreck/accident

People is plural, so you would write: "Do British people say "a car wreck" instead of "a car accident." The locution "car accident" sounds rather contrived to me. I'm an American, but i believe that the British would say "a car crash" rather than either wreck or accident. Americans would be likely to say "a car wreck," and if they used accident, they would very likely not modify it with car. So, if i say: "Did you hear? Thomas was in an accident."--speakers of the American language would understand it to mean an accident in an automobile. However, if i said: "Did you hear? Thomas had an accident."--an American would probably ask what kind of accident, but would not think of an automobile accident.

Thank you, Sentanta.

Do you man British language?

No, i meant the American language. The Americans and the British both speak English, but they speak it in ways which are sufficiently different that it is not inappropriate to speak of the American language.

not to de-rail or presuppose any significant eligibility as an expert on the language, but I did spend the last week as an interpreter for some English people in rural Missouri, and there are some interesting differences.

Car accident, in my view.

Certainly not wreck.....possibly crash.

Sure. Trains wreck; cars crash.

Sometimes smash.

In British English, (which is what the questioner was asking about), trains and cars "crash" (verb), they can also be in "crashes" (noun), in which they are "wrecked" (verb). British people often hear and read about Americans who sadly are in train and car "wrecks" (noun). In the 19th and early 20th centuries, trains were often in "smashes". (At my school, a certain dish, a stew containing tomatoes, was known as "train smash") In formal British English, as seen in e.g. police, medical and insurance reports, one might see "road traffic accident", often abbreviated to "RTA".

Trains don't just "crash" into (collide with) other trains or obstacles on the line; they also figure in other types of incident such as derailments, etc, which, strictly speaking, may not be "crashes".