The presiding judge, ordering them to serve at least 40 years behind bars, said he believed that both attacks -- on July 7 and July 21 -- were inspired by the al-Qaeda terror network.

The four -- ringleader Muktar Said Ibrahim, as well as Yassin Omar, Ramzi Mohammed, and Hussain Osman -- were found guilty of a failed bid to set off four bombs on underground trains and a bus -- the same scenario as on July 7.

"I have no doubt that they were both part of an al-Qaeda-inspired and controlled sequence of attacks," said Judge Adrian Fulford at Woolwich Crown Court in London.

"This was a viable, indeed a very nearly successful, attempt at mass murder. It was long in the planning and came soon after July 7. It was designed for maximum impact."

He noted that prosecutors had not attempted to demonstrate a "direct link" with the July 7 attacks, in which suicide bombers killed themselves and 52 innocent people on the underground network and a bus.

But he said the July 21 failed attacks were "nearly a carbon copy of that event exactly two weeks later," adding that "what happened on July 7 2005 is of considerable relevance.

"It demonstrates the lethal effect of this plan had it succeeded.

"It is clear that at least 50 people would have died, hundreds of people would have been wounded, thousands would have had their lives permanently damaged, disfigured or otherwise, whether they were Christian, Muslim, Jewish, Hindu, Sikh, Buddhist, agnostic or atheist."

The sentencing came shortly after prosecutors confirmed that two other defendants in the case will face a re-trial, after jurors failed to agree a verdict on Tuesday.

Ibrahim, 29, admitted in court that he was the ringleader but said he used a harmless device intended only to protest against Muslim suffering, especially in Iraq. The other convicts also claimed the devices were harmless.

Peter Clarke, head of the Metropolitan Police's counter-terrorism unit, praised the jury for rejecting such "ridiculous" lies.

"These men are dedicated terrorists who no longer pose a danger to the public, but recent events have shown that the threat from terrorism is, at the moment, ever-present," he said Tuesday, referring to failed attacks in London and Glasgow.

Speaking after the sentencing, the head of the Crown Prosecution Service's counter-terrorism division, Susan Hemming, said the four could have been "in no doubt" over the consequences of their actions.

"While the implementation of their plan was incompetent, their aim was clear: they wanted to kill and maim on a massive scale," she said in a statement.

"Exactly two weeks after the terrorist attacks on 7/7 they targeted the same transport system and tried to cause the same level of death and destruction.

"They knew what would happen. They had seen the death and destruction of 7/7 and the fact that they continued with their plan showed their brutal intent."

Meanwhile authorities were investigating why Ibrahim was able to travel to Pakistan for terrorist training barely six months before the 2005 attacks, despite being known to police.

Ibrahim travelled to Pakistan in December 2004, and was there at the same time as Mohammed Siddique Khan and Shehzad Tanweer, two of the four suicide bombers in the July 7 attacks.

"I'm looking very carefully at the circumstances that surround his visit to Pakistan," said Prime Minister Gordon Brown.