Bombers left a trail of carnage across central London yesterday as the capital became the front line in the war against terror.
Four huge bombs left people dead, dying and horribly maimed in a "barbaric" series of coordinated attacks carried out on the city's transport network without warning.
One police source indicated that 41 people had perished and 95 were seriously injured.
Scotland Yard officially confirmed that at least 37 people were killed and there were 700 casualties, 300 of whom were taken to hospital by ambulance.
Death and destruction rolled across central London in 60 terrifying minutes as world leaders sat down to business in Scotland at the G8 summit.
Seven people died in the first blast in a Tube tunnel 100 yards from Liverpool Street Station, 21 died in a blast between King's Cross and Russell Square, and seven died at Edgware Road station in an explosion involving three trains.
Exactly 30 minutes after the Edgware Road blast, a bomb tore the roof off a double decker bus packed with commuters forced above ground after the Tube network had been shut down.
Hospitals were deluged with hundreds of people suffering with blast injuries and doctors and paramedics battled to save the most critically injured on streets and Tube train platforms.
Tony Blair pledged that Britain would not be intimidated by the terrorists and promised intense police and security service action to bring the bombers to justice.
He said: "They are trying to use the slaughter of innocent people to cow us, to frighten us out of doing the things that we want to do, trying to stop us from going about our business as normal, as we are entitled to do and they should not and they must not succeed.
"When they try to intimidate us, we will not be intimidated. When they seek to change our country or our way of life by these methods, we will not be changed."
He added: "The purpose of terrorism is just that. It is to terrorise people and we will not be terrorised."
A group calling itself the Secret Organization Group of al Qaida of Jihad Organization in Europe claimed responsibility for the attacks on an Islamic website.
It read: "O nation of Islam and nation of Arabism: Rejoice for it is time to take revenge from the British Zionist Crusader Government in retaliation for the massacres Britain is committing in Iraq and Afghanistan.
"The heroic mujahidin have carried out a blessed raid in London. Britain is now burning with fear, terror, and panic in its northern, southern, eastern, and western quarters."
The outrage echoed the al Qaida assault on Madrid commuters in 2004 in which almost 200 people died.
The blasts were initially blamed on a power surge but it soon became clear that it was a co-ordinated attack on the capital.
The explosions were condemned by all G8 leaders as "barbaric".
Speaking at Gleneagles, President George W Bush vowed that the terrorists would be brought to justice.
The Queen spoke of her shock at the "dreadful events". Buckingham Palace said she would be making a visit today to meet people involved in the tragedy to express her support.
But Respect MP George Galloway said Londoners had "paid the price" for Tony Blair's decision to go to war in Iraq and Afghanistan.
He called on the Prime Minister to withdraw the British troops from Iraq in order to remove people in the UK from "harm's way".
* Scotland Yard has issued the following casualty hotline number: 0870 1566 344.