I've asked this before and never got a straight answer, but I'll ask again: what exact clauses do I need to modify in the employment contract, and what exactly must they say, in order to avoid this sort of situation? (relevant to UK employment that is). If you've solved this for yourself, please tell us all how and what it's written in yours so we can do the same. Here is a link to what my previous employment contrac…
The only exception to this is if the work you are doing outside the contract conflicts/overlaps with the work you are doing within the contract. In that case, if the employer inserted a restraint of trade clause into the contract, that would be enforceable (that is a standard non-compete, which is perfectly legal and sensible).
It is all total nonsense though. UK employers, and lawyers, are a bit mad about this kind of thing. They will insist on things like probationary periods or working "at will" for a period of time...and then they will demand that you yield 24 hours of your time whether awake or asleep to them...whilst they pay you for 7 hours. It is what happens when underemployment is high.