I am no lawyer but having seen a few "Cops with Cameras" documentaries and from other sources:

I would say that Joe's three things apply much the same in Brittain.

I know that you cannot search a property without a warrant. And doing so would screw up any court case, unless there was good evidence that permission had been given by the occupant (like a video!). I guess searching a person is different, for the safety of the police.

Much like a bailiff needs the consent of the occupant - though once given can force entry multiple times. Or must seek a warrant.