Being cynical I think they are using the fact that terrorism took place
on the tube and that is therefore easier for the police to undertake
operations in that environment that they could never get away with if
they did them on Walthamstow High Street.

Indeed I've always though it was noteworthy that William Bratton, he of
zero tolerance policing fame, developed his ideas while head of the NY
Transit police. Personally I would accept a much higher level of
policing intrusion while using the transport system than I would in the
rest of my life.