I dug up the following:
Copyright, Designs and Patents Act 1988
Section 62:
This section applies to—
(a) buildings, and
(b) sculptures, models for buildings and works of artistic craftsmanship, if permanently situated in a public place or in premises open to the public.
(2) The copyright in such a work is not infringed by—
(b) making a photograph or film of it
First I thought that would give you the right to take pictures. Appearantly it doesn\'t cover painting and murals though. Also even if it did I assume the murals could be regarded as temporary, and therefore again not covered. You weren\'t taking pictures of \"fixed\" sculptures were you? That is allowed.
You could have tried Section 29 or 30 - that it is legal to do \"fair copies\" of copyrighted material for reseach or private study, or for the purpose of a news report or for criticism or review. If you said it was for uni it may have added weight to this. Again though if the officer had \"reasonable belief\" that this was not true, or if you took \"more photo\'s than reasonable\" it could be considered unlawfull.
I guess it is possible for you to have been arrested but I doubt it would get anywhere in criminal court. Ch.48 details criminal (rather than civil) offences.
For a criminal offence they\'d have to show you were intending to sell, distribute or make available to the public what you took pictures of (that is if we are talking about art). I guess the police officer could have said he had reasonable grounds for believing you were taking pictures to distribute or sell on, but getting that to stick in a court seems pretty far fetched to me.
It seems a bit extreme. I think he \"could\" have arrested you but with no real chance of a conviction, you have to ask why??? Seems a bit stupid and petty. Incidentally it appears only officers of HM Revenue & Customs can \"seize\" the copyright material on the spot and not return it. Police seem to have to keep it and present it to the court.... Perhaps that\'s why he asked you to delete it - he had no powers to take it off you unless he made an arrest. Perhaps the threat of an arrest was just a bluff (knowing that an arrest would be a waste of time)?
Anyway take this with a pinch of salt I have no legal qualifications. To me it seems a bit extreme though and just a plain over-reaction and a bit crappy.