News item from 2 April at AP
here.
Police and private security staff hassling people who conduct photography in public places is an ongoing problem.
A
BJP article on the same subject.
This issue has cropped up before and AP has campaigned for the police to be enlightened. More news stories linked at the bottom of that one, AP forum discussion
here.
It is interesting that the rozzers are well versed in (and keen to action) laws that suit their agenda but not those pertaining to civilian rights. There is a disturbing number of unnecessary and repressive actions taken under the guise of anti-terrorism. AFAIK they cannot normally demand your film/memory card or erasure, it's private property. You need to know your rights, see the link further up this thread.
Input from non-UK contributors seems to confuse the matter in a UK-specific thread and forum like this (no offence intended).