BBC World Service have just reported that Arab sources are saying it is Al-Q... although the modus operandi (multiple simultaneous attacks) already made that very likely.
It's very unlikely to be anti-capitalists or the IRA, as it is not the anti-capitalists style and the IRA are unlikely to take part in an attack like this nowadays.
I've already checked with my family in London and they're okay, apart from one who can't be reached (mobile is off) who could have been nearby. Mark you, I've been within 300 yards of an exploding post box and a nephew of mine was 1/2 mile from the Bali bombins so nearly getting blown-up is something of a family tradition. My mother sheltered for a few minutes in a shop door way on her way to an air-raid shelter during the Blitz - when she came out there was no doorway, let alone any shop...