Analog Kid at Random Nuclear Strikes asks:

Do you think the vast array of surveillance cameras in London helped even a tiny bit?

Security expert Bruce Schneier has this to say:

I was going to write something about the foolishness of adding cameras to public spaces as a response to terrorism threats, but Scott Henson said it already…

Henson has been blogging on this topic for quite a while and points out that when private businesses install cameras they can have some success.  When governments install cameras in public areas they have little positive effect.  England has millions of cameras but they are now to the point of outlawing certain types of clothes that thugs use to easily defeat the cameras.  And as long as you are allowed to wear clothes and carry backpacks, shopping bags, and brief cases in public there will be no surveillance system which can prevent crime or especially prevent terrorist activities.  Spending the resources on better intelligence and destroying the culture of terrorism is a much wiser plan of action.