I don't know about the UK but rarely will you get a ticket for going only 5mph over the speed limit in the US. And as the man was trying to get OFF the road to avoid an accident and tend to his wife - I'd say he has a good shot at winning in court.
If you're under duress then your mind is not on the road. You are a liability to yourself and all of the other drivers. So yes, the fine (whatever it is) is appropriate.
Should have called a cab, family member, friend, etc. to drive.
They are no circumstances where anyone can legally break the speed limit. Even the emergency people like fire/ ambulance etc. are supposed to obey all traffic laws. They get away with speeding/ going through red lights (must be done with care) etc. because its socially allowed.
Duress can be a defence to any criminal charge which requires an intent to commit it.Speeding involves 'strict liability'. Technically your intention or state of mind doesn't affect legal liability.This case does not really involve duress.Speeding whilst someone held a gun to your head would be.
That apart this chap should definitely have been given the benefit of the doubt.There used to be some notion that the decision to prosecute was only take in the public interest and where the public interest did not require it the matter would be dropped."Zero tolerance" has its place but not here.