HOWZAT

He said: "The level of forensic evidence will be extremely high, much higher than last time. They will have the devices and much can be done to them in terms of fingerprinting, DNA, the origin of the detonators and where the bags were bought. If this was a series of dummies deliberately timed to cause mass panic then it puts the people responsible at considerable risk of being found."

Professor David Capitanchik, a terrorism expert based at Robert Gordon University in Aberdeen, warned that today’s explosions may have been "amateurish" devices deliberately aimed at emergency services who arrive at the scene. He said eyewitness reports of small explosions in a rucksack could indicate that they were not intended to explode properly until they had been recovered.

"It appears as if the detonators have gone off, but reports indicate a much more amateurish-made device than the bombs two weeks ago," he said.

"In other parts of the world which have experienced incidents like July 7 in London, smaller bombs have later been put in places with the hope that they will go off when the police and emergency services examine them. This indicates that in today’s situation the police are going to take a great deal of time and exercise great care, as there is a possibility that these bombs are intended to entrap police and emergency workers."

All were agreed, however, that today's attacks would add to the fear, which had been beginning to subside. Mr Ayers said that although casualties appear to have been avoided, the long-term damage to the city's psyche may take even longer to heal.

Mr Clarke said: "It is entirely plausible that they will have planned a campaign, not just one bomb. It’s part of terrorist psychology that one bomb is never enough.

"You gain the effect that you want by creating a sense that there are lots of bombs and the public are going to have to live with this for a long time, unless they do something, unless the government changes. The second event is a prerequisite to the psychology of a campaign ... This important because it’s momentum for terrorists."

Former government intelligence officer Crispin Black agreed that those who planned the attacks were trying for the maximum psychological effect.

Speaking outside the police cordon surrounding Warren Street tube station, he said: "It could be that this is a nasty sort of copycat attack mimicking what happened two weeks earlier but not using quite the power of explosives, but still getting the chaos and fear effect as you can see around us.

"In this stage of a counter-terrorism campaign you’re bound to get the feeling that rings are being run around us."

Mr Black said this will be the case until intelligence on all the attacks improves. But he said incidents like today should help police catch the perpetrators.

"In this kind of attack it looks as thought the terrorists have put their heads above the parapets and that falls into Scotland Yard’s hands," Mr Black said.

"It then becomes much easier for police to start tracking them down."

He added: "It’s too early to tell who these people are but even if they’re just copycat attackers that’s a pretty depressing thing to think about, that there are young people out there who are so radicalised they are prepared to bring London to a kind of taunting halt. And that’s the best scenario."

Explore UK News

• Crime News

• Education News

• Health News

• Scotland News

Times Recommends

• Foxy Knoxy snared by her lust and her lies
• Britain is the land of the shrinking family
• Zac Goldsmith: Not such a green god