Last updated: 25 October 2008
For the last thirty years Londoners have had to learn to live with the possibility of the car bomb. We have had to be vigilant but we have also got on with our lives.
Now we have to be prepared for any eventuality and any emergency. The threat to London from terrorism remains real and serious.
As Deputy Chair of London Resilience, and as chair of Transport for London - which now runs London Underground - I think it is right that we test our emergency responses.
This is not alarmist - nor is it a response to any specific threat.
Indeed there are many other practical lessons which we can learn from working together in a complex environment such as a major transport interchange.
Today's exercise is simply a demonstration of our commitment to the safety and security of Londoners and everyone who visits our city.