By Nick Assinder
Political Correspondent, BBC News website
This was just the sort of terror attack Tony Blair has dreaded and the thought of which, he said, kept him awake at night.
Time and again, ministers and security chiefs have said an attack on the UK was inevitable - it was a case of when, not if.
Tony Blair leaving the G8 summit
It came at a time when the eyes of the world were on the UK, as Mr Blair hosted the G8 meeting in Gleneagles.
To that extent, the perpetrators succeeded in securing the greatest possible global impact.
But Tony Blair has also insisted that, when the inevitable attack came it must not succeed in demoralising or dividing the country. That would be to hand the killers victory.
And, like successive prime ministers and opposition leaders before him, he has declared that would never be allowed to happen.
He drove home that determined message from the G8 summit, declaring: "They will never succeed in destroying what we hold dear in this country."
The IRA campaign - including the attempt to kill Margaret Thatcher and her cabinet in the Brighton bomb in 1984 - is still fresh in Britons' minds.
And throughout that campaign, citizens and political leaders remained united in their refusal to buckle.
In the immediate aftermath of the London attacks, politicians including Conservative leader Michael Howard and Liberal Democrat leader Charles Kennedy united to insist the terrorists would not succeed in their aim of demoralising the nation.
Mr Howard said: "What is important is to make it absolutely clear that this country is united as one in our determination to defeat terrorism and to deal with those who are responsible for the dreadful acts that have taken place in London".
On many occasions Mr Blair has defended plans to toughen up anti-terror laws by saying that the day after any such assault, people would ask if he had done everything in his power to stop it.
They would not, he said, be raising civil liberties arguments.
It is certainly the case that there will ultimately be questions about whether the attacks could have been averted.
The truth, of course, is that no leader can ever guarantee security measures will be enough to stop an attack. That is the nature of terrorism.
IRA tried to kill cabinet
The arguments over identity cards and detention without trial will take on a new urgency as ministers consider any new measures to take in the wake of the attacks.
There will also, needless to say, be questions over whether the war on Iraq made attacks on the UK more or less likely.
But the history of such terror attacks in the UK suggests that, in the short term at least, people are more likely to unite behind the government.
All these doubts and fears will be raised in the future. For now politicians are united with a common determination not to yield or indeed, over-react, to the bombings.