I spoke to one of the Ford mechanics, he said that this was a fairly common problem, in fact a mate with a fairly new 1.6 focus said she has the same problem from time to time.
Apparently it is due to slight flooding of the engine, so if you depress the accelorator for a few seconds and restart, it should be fine. Seems to have worked so far....
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Escort 1.6GLE, Escort 1.3, Fiesta 1.3, Fiesta ST!