Didn't they ban DSLRs being used? I half remember something on the AP website and a fuss was made about the whole thing.
*digs around on the Internet*
Found it!
http://www.amateurphotographer.co.uk/photo-news/534467/dslrs-banned-from-aldwych-tube-stationDSLRs were banned because of the high quality sensor and resolution! So presumably a Leica M, Fuji Pro X1, Olympus OM-D and even the Canon G1X are allowed? They're not DSLRs after all.