had one of the same type of van outside my unit on private ground
Clear bit of trespass there. Law Enforcement agencies can only enter private land on authorisation of a Deputy Chief constable (or equivalent - the Police Act 2002? Can't see that they'd have that for a routine sweep.) The Road Traffic Act might give them some right of entry but I think this would be limited.
He could have lodged an appeal, though the complexity of it would probably have involved legal advice of some sort and the associated potential cost. Nasty business if they have overstepped the mark. Might be worth a letter querying under what power they entered your premises.