I've been watching BBC on the tele, and it seems these might have been "real" bombs which failed to detonate properly. The plus side of this is that they've already got two suspicious buggers outside of Whitehall & No.10 Downing, and the others are running loose (rather than being terrorists turned into paste). Catch them and we have a lead to the asshole running this operation. Of course, I say "we", but I suspect the SAS might get there first...
