However shocking the four attempted bombings in London yesterday, there are few who did not wonder whether there would be a second wave of suicide attacks. As in Madrid, the terrorist aim was clearly to send a message of defiance, to prove that they can still strike at will and to create panic in a city only just beginning to get over the terrible events of two weeks ago. In Madrid they failed because they were surrounded and blew themselves up. In London, they appear to have failed through ineptitude: no bomb exploded, there were no fatalities and the emergency services were extremely quick to reassert full control.

For all the relief that no lives were lost, no one should downplay yesterday’s attacks. This was clearly an attempt not simply to disrupt but to kill. The patterns were similar. Public transport was again the target. The same attempt seems to have been made to explode simultaneously bombs hidden in rucksacks. Was this too big an operation for any copycat extremists to mount in the days since the atrocities on July 7? Were the terrorists recruited by the same network of extremists to act as a follow-up wave? The awful implication is that among Britain’s Muslim community there are still men prepared to kill for what Tony Blair yesterday called “an evil, bankrupt ideology based on a perversion of Islam”.

The Prime Minister again struck the right note yesterday. He called on people to get on with their lives and not to allow themselves to be intimidated. And, with the powerful support of John Howard, the visiting Australian Prime Minister, he refuted attempts to lay the blame on Western policies in Iraq, the Middle East or elsewhere. “The people responsible for terrorism are terrorists,” he said.

Londoners — and indeed Britons in other cities — will have to maintain their vigiliance for a long time to come. There will be more bomb scares, and there is a need for patience and stoicism. The police were lucky in having clear leads that took them to the network in Yorkshire. Yesterday’s botched bombings should provide a rich harvest of clues, which will be revealing about particular individuals and broader networks. What is becoming clear is that extremism has taken hold among a minority of Muslim youths, who have links with extremists overseas, especially to some of the madrassas in Pakistan that have become virtual training camps for suicide bombers.

Forensic evidence from the Underground and the bus in Hackney may give vital clues to the origin of the explosives and detonators. But what is needed more than anything is sustained, institutionalised intelligence.

This can come only from the community within whose ranks the extremists emerge. Mr Blair won reassurance from Muslim leaders at his Downing Street meeting earlier this week that they would do what they could to root out the fanaticism that is bringing fear to their community and dishonour to their religion. But, as both he and they recognise, more is needed.

There must be an unremitting campaign against the preachings of nihilist fanatics winning converts among young Muslims. And there must be a better understanding of who is most vulnerable to these intolerant teachings. Furthermore, there must be better intelligence on the link to extremists in Pakistan. And, for years to come, there must be sustained vigilance by police and public alike.