The Guardian is running a blog updated throughout the day with more information.

It is important however that those engaged in terrorism realise that our determination to defend our values and our way of life is greater than their determination to cause death and destruction to innocent people in a desire to impose extremism on the world. Whatever they do, it is our determination that they will never succeed in destroying what we hold dear in this country and in other civilised nations throughout the world. – Prime Minister Tony Blair

I want to say one thing: This was not a terrorist attack against the mighty or the powerful, it is not aimed at presidents or prime ministers, it was aimed at ordinary working-class Londoners…That isn’t an ideology, it isn’t even a perverted faith, it’s mass murder. – London Mayor Ken Livingstone

The first link is courtesy of Boing Boing.