Hi Simon. Coincidentally, I was talking with a friend about the Tate last night. My friend's mother is over from Poland for a couple of weeks and I have to host them for a day somewhere in London next week. The Tate cropped up as an idea so I might suggest this to them.
Some of the subject matter is a little risque, and the sneaky techniques morally dubious, but some really amazing photos and alot of them!
More information here:
http://www.tate.org.uk/modern/exhibitions/exposure/roomintro.shtm