Having spent 6+ years in the USAF as a weapons specialist (IYAAYAS), I know a bit about explosives and weapons. If I witnessed a bombing I would help the injured. If I witnessed strange sounding low-order explosion, more like a thump than a bang, I would run upwind as fast as I could for as long as I could. Low-order explosions are THE way to spread bio/chem weapons. I don't think that is the case in London, it sounds more like bad bomb making to me.
I know what you mean and agree with you. An obvious high order explosion would generally preclude biowarfare and helping others would be just fine. A low order explosion raises a lot of questions - but this one appears to be incompetence rather than bioweapon dispersal mechanism, fortunately.
Let's see, we've gone through the Al Queida "A" and "B" teams, apparently; this must be the "C" team.