In the UK people are not prosecuted for what they might have done.
Correct - they are charged with what they
have done - and the police officer in question admitted to careless driving.
He was in a position where
he knew full well what he was doing was illegal and against his training, but he still did it.
He was charged, pleaded guilty and was sentenced accordingly.
Obviously I am missing something, unless you are condoning his actions and using the argument of "the ends justify the means".
You seem to indicate that he committed a minor crime in the pursuit of someone he
suspected of committing a more serious crime.
Would you say to these victims that 'careless driving' is a minor crime:
http://news.bbc.co.uk/1/hi/scotland/north_east /8067898.stm