The UK police have been foiling attacks at the rate of close to one a week since at least Iraq if not earlier. That's in effect what some counter-insurgency spook was saying on the news earlier.
One of the reasons we've been doing so well at it until now is that we let the loudmouths run around feeling safe so that we can watch them. Our security services, during the long campaign against the IRA learned not to lightly trade good human intelligence for politically visible "results."
I'm confident that the perpetrators will either be arrested by the police, or more likely, will be quietly shot by SAS.
I have no doubt that your security services are the best in the world, which is why these attacks have not happened sooner and more often. Still, there's very little to be done about a suicide bomber unless you catch him in the act.
I suspect that Al Quaeda and their associates will take this tack now in Europe and the U.S. now that the terrorists are strapped for cash and being watched closely.
This is the only type of attack they can pull off.
Which, in itself, is a great credit to the security forces in both our countries.