*But unless there is an actual definition of what are and are not legally acceptable reasons to go to work, how can anyone, be they the police, the courts or the individual, decide if the person 'could' have worked from home?
Yes, laws are open to interpretation, but there still have to be clear parameters. You simply can't fine people because 'in your view', they 'could' have worked from home.
Obviously this silly 'law' doesn't bother you, but generally speaking, would you be happy to be fined because of the subjective 'views' of the individual police officer who pulled you up?*
As I said, individuals have to use their common sense and hope that police use theirs. It's how many laws are enforced.
For example, the Public Order Act doesn't list out what behaviour does or doesn't cause alarm or distress. That too is obviously subjective but just because there is a spectrum of possible behaviour, it doesn't mean we shouldn't have laws against bad behaviour.
I'm perfectly happy for the police to use their judgement because
the alternative is to live in a nightmarish 'computer says no society'.
If you tried to define it precisely, you would get silly results so it is best left to people to make a judgement on a case by case basis.
If you have any reasonable excuse to go to work, you will be fine. My guess is that there will be very few fines given out and they will be to people who admit they could work from home but chose not to.