LONDON was lucky not to suffer heavier casualties, according to a Stonehouse-based security expert.

Alex Bomberg, head of the International Intelligence security firm, said the outrage bore all the distinguishing features of an organised al Qaeda cell.

"To be honest, we were very lucky," he said.

"We lost 191 people in the Madrid bombings and I think if these bombs had gone off 20 to 30 minutes earlier it could have been a lot worse.

"I am absolutely convinced it was al Qaeda. The timing of the bombs was impeccable - they went off within a minute of each other and hit multiple targets.

"There is also the fact that no parts of the device have been found yet."

Mr Bomberg, a member of national defence and security think-tank the Royal United Services Institute, said the attack was likely to have been masterminded by a small cell of five to 10 individuals.

"You would have the bombers themselves and the quartermasters, who prepare the bombs," he said.

"Often you have a recce team, who probably live locally and scout out locations and routes."

He said that even if security services got a man inside the organisation, he would probably never meet the bombers, making identification doubly difficult.

But he added the terrorists had not achieved their main aim of cowing the London public, who seem determined to use public transport as normal this week.

"I would say it has stiffened people's resolve a great deal," he said. "People are using transport at nearly its normal level.

"People are saying it's going to take more than this to change public opinion, which is exactly the right reaction."