So I started the day with the same ill feeling in my stomach as the Challenger explosion, Sept 11th, and Madrid...but now at work, this excerpt from http://news.bbc.co.uk/1/hi/uk/4659511.stm struck me as something to remember:
Mark Easton : King's Cross : 1820 BST
Just after 0900 I looked out of my car and saw the soot-blackened faces of men and women who might have been trapped underground from some time. I did fear how the day might unfold.
I parked my car just a few hundred yards away and heard a thunderous boom echo down the road. I didn't know it then but it was blast that ripped the roof off a double decker bus.
At King's Cross the professionalism and control of the emergency services was impressive, and the mood was one of calm, as if they'd managed to suck the terror out of terrorism. If yesterday was about the euphoria of winning the Olympic Games - today is about the horror of losing so many lives in Central London.
But if this was the work of al-Qaeda trying to terrorise Londoners, my impression from King's Cross is that they failed.