Following the Al Qaeda attacks on Sept 11 in America, we've conducted a series of exercises in London in order to be prepared for such an attack.
One of those exercises, which was done by the government, my office and the emergency and security services, was based on the possibility of multiple explosions on the transport system during the rush hour.
And so the plan that followed from that exercise is being followed today - with remarkable efficiency and courage, and I praise those staff who are doing that.
I'd like to thank Londoners for the calm way they've responded to this cowardly attack. Do not travel. Take the advice of the police. Stay at home.
If you're not at home, wait until you hear the advice over the radio or television from the police on how to get home later today.
I have no doubt whatsoever that this is a terrorist attack. We did hope in the first few minutes after hearing the events on the underground that it might simply be a maintenance tragedy. That was not the case.
I have been able to stay in touch by the very excellent communications that were established for the eventuality that I might be out of the city at the time of the terrorist attack, and they have worked remarkably.
And I will continue to be in touch until I board the plane that takes me back to London in the next few hours. I want to say one thing specifically to the world today.
This was not a terrorist attack against the mighty and powerful, it was not aimed at presidents or prime ministers. It was aimed at ordinary, working-class Londoners, black and white, Muslim and Christian, Hindu and Jews, young and old; an indiscriminate attempt to slaughter, irrespective of any consideration for age, for castes, for religions, whatever.
That isn't an ideology, that isn't even a perverted faith. It is just an indiscriminate attempt at mass murder. We know what the objective is. They seek to divide Londoners. They seek to turn Londoners against each other.
I said yesterday to the International Olympic Committee, this city of London is the greatest in the world because everybody lives side by side in harmony. And Londoners will not be divided by this cowardly attack.
They will stand together in solidarity around those who have been injured and those who have been bereaved. That is why I am proud to be the mayor of that city.
Finally, I wish to speak through you, directly, to those who came to London today to take lives. I do know that you do not fear to give your own lives. That is why you are so dangerous. But I do know that you fear you may fail in your long-term objective to destroy our free society.
I can show you why you'll fail. In the days that follow, look at our airports, look at our seaports, and look at our railway stations. And even after your cowardly attacks, people from the rest of Britain, people from around the world will arrive in London to become Londoners and to fulfil their dreams and achieve their potential.
They choose to come to London, as so many have come before, because they come to be free, they come to live the life they choose, they come to be able to be themselves.
They flee you, because you tell them how they should live. They don't want that. And however many of us you kill, you will not stop their flight to our cities where freedom is strong and where people can live in harmony with one another.
Whatever you do, however many you kill, you will fail.