I am not sure if y'all have seen this, but...

[niner]

Police delete London tourists' photos 'to prevent terrorism'

http://www.guardian.co.uk/uk/2009/apr/16/police-delete-tourist-photos

Also, I am not sure what kind of source the Guardian is, but seeing some of the news reports coming out of London, lately, I can believe it.

[Tdragone]

If they had another memory card they could just stow that one and recover the pictures later.

It IS sad what photographers are being targeted for now though!

[NinetyEight]

The police are not allowed to delete files or pull out films etc. - If they suspect anyone of anything they can arrest them on suspicion and get the files/films examined if they please. (also deleting files could be destroying evidence).