When police are involved that's one of those 'get in line' situations. I suspect the UK authorities are far more worried about the potential for destruction of evidence that they are in hampering an 'investigation' by FB.
I would think it was very likely that Facebook itself seeks to destroy evidence. They've got a much clearer sense of their culpability than any outsider would.
No, when police are involved that's one of those 'maximally invoke your rights' situations. The police are the enemy. Get whatever brigade of lawyers you can afford and stop their efforts in any way you can. This is true whether you're an unfortunate person who happened to be driving while black or a multinational corporation.
