The bottom line on responding to terrorism is not giving the terrorists what they want. Not that we should build policy around pissing bad guys off just because, no matter what it costs us. It's that we can't encourage bombings. I suspect part of the reason there hasn't been another attack on the US since 9/11 is that they backfired, causing the US to invade two Middle Eastern countries. After they got a withdrawl from Spain, they must have thought they could get the same out of Britain. By all indicators, they'll be wrong. I don't want to be too hard on the Spanish; they didn't want to be in Iraq in the first place, the Socialist party was promising withdrawl all along, and part of the backlash was how the government handled the attacks, not that the government's policy encouraged them. Also, the London bombings probably would have happened anyway. But shrinking in the face of terror is a mistake.
Also, thoughts on the British response from the Chritian Science Monitor. Key quote, from London' mayor: "In the days that follow, look at our airports and seaports, and even after your cowardly attacks, you will still see people from around the world coming to London to achieve their dreams." That's the way to do it.