The Al Qaeda freaks have zero political acumen. They should have just kept trying to destabilize Iraq and left the West alone. Eventually, our weak-kneed, no-policy-but-an-anti-GOP policy lefties would have managed to turn Iraq into another Vietnam and we'd be out of there just in time to welcome in a Hussein clone or even the man himself. Instead, they hammer the U.S.'s biggest ally. Error. More dead westerners with whom Americans strongly identify will simply mean a new infusion of determination.
This action looks like an unforced error. Why not let America's left-wing nuke the enterprise through constant agitation? The answer is that the error may not be unforced. The Afghan/Iraqi projects may be going well enough that Al Qaeda had to introduce a desperate gambit like this one. If they could make Britain "do a Spain," then America would truly seem alone and would be harder pressed to continue. Won't happen, fellas. You've given us what we need to marginalize the "hate America" Americans and the Bush-hating Eurofashionistas.
As S.T. Karnick would say, "Many thanks."