PCPaul wrote:

From my reading around it looked like you need an infeasibly good image
to be allowed to use it in court (for example - head and shoulders
filling 50% of the frame). I'm no expert though - that may be paranoia..

There's a Home Office guidance document on the use of CCTV in evidence.
I'm not sure it it's public domain thought. I think it is because it was
intended for the guidance of CCTV operators in shopping malls as well as
building security.