I imagine it's worse for you because of 9/11 flashbacks, but we're ok. Seriously. London has been dealing with bombs since the Blitz in WWII. We had the IRA blowing up parts of London and SE England for 25 years, forgodsake. Even despite their ceasefire, we still have reinforced post boxes and litter bins on the streets, and no litter bins on public transport. (This was the thing that amazed me most about recent travels in the US - the authorities claiming they were afraid of attack, yet there were bins everywhere - even in the airports!)
I grew up halfway between Sandhurst Military Academy (where Prince Harry is going) and Aldershot, the home of the British Army. We had a bomb scare every other week, and about 1/4 of them turned out to be real bombs. Evacuating Marks & Spencer to go and sit in McDonalds for half an hour until we got the all-clear was just what we did. You just pay attention to any unattended bags or packages, and get on with it.
I remember the Selfridges bomb, the bomb on the rail line between Brookwood and Woking, the Canary Wharf bomb, the bus that blew up along the Strand... all ones that people I know were caught up in. Only a few years ago, a lone nut decided to nailbomb parts of London associated with ethnic minorities and queers - the bomb blowing up the Admiral Duncan pub in Soho affected me deeply, not least of all because Richard's work is just round the corner from it and one of his co-workers only narrowly escaped injury. But we survived. The pub is still standing, and features a memorial to the people who died - and I urge anyone interested in queer history to go there and see.
We've had terrorists, nuts and loons for longer than I've even been alive. This is just another one of those things. It's tragic for the families of the people killed, but they can't get us all. They didn't manage it in WWII. They won't manage it now.
P.S. I don't often agree with him, but Go Ken!