The flypaper theory is dead and buried. The idea that going to war in Iraq would prevent attacks in the west is going to hold precious little currency now. This is important: it isn't stated much, but this is a fundamental justification for the Iraq war as a component of the WoT.
Also, the CIA/NSA/MI:5/MI:6 agencies are going to endure serious criticism and critiques. Make no mistake: if the Americans had an inkling, the Brits would have known, and thus there's no doubt that the Americans didn't know either. This was an intelligence failure and a big one, and it was under the watch of Bush and Blair's intel services. I would not be surprised if the attacks are levelled at those within the agencies who aren't "playing ball"- certainly that's the way it's worked to date- but then again, this is different than the 9/11 or Iraq failures, as it speaks to a core foreign policy goal of the Bush administration and Blair government.
Blair's going to be a target too- not only because it was his watch, but because there's going to be an undercurrent of belief that this has to do with the U.K.'s visible and open support of the U.S. A weak PM is going to be much, much weaker, unless a "rally 'round the flag" effect builds him up. I've never got the impression the UK worked that way- a PM isn't a president.
Not sure whether the UK is going to start having domestic turbulence. A LOT depends on how official Britain handles this, and it looks like they're try to prevent anti-Islamic reprisals (and, in turn, "defensive" acts by frightened British Muslims.) The calm public reaction would seem to imply otherwise as well.
Finally, my support and sympathy to those affected by the bombings and Londoners in general. I hadn't mentioned that before, but rest assured of it.