The four men convicted of the attempted bombings in London on 21 July 2005 have each been sentenced to a minimum of 40 years in prison. They were told that their al-Qa'ida-controlled plot was a "very nearly successful attempt at mass murder".

Mr Justice Fulford QC, sentencing the four former refugees to life imprisonment yesterday, said it was clear the foiled attacks were part of a sequence started by the July 7 bombings, which killed 52 people two weeks earlier. If the July 21 bombers had been successful they would have killed or maimed hundreds of people using London's transport system and blighted the lives of thousands, Woolwich Crown Court, in south-east London, was told.

The convicted men - Muktar Said Ibrahim, 29, Yassin Omar, 26, Ramzi Mohammed, 25, and Hussain Osman, 28 - showed no emotion as they were told that none of them would be considered for release before 2047. All four men, who were found guilty of conspiracy to murder for trying to blow up Tube trains and a bus, came to Britain as refugees from countries in the war-torn Horn of Africa and were allowed to stay in the UK or were granted British citizenship.

Mr Justice Fulford said he accepted that Ibrahim, the self-declared "emir" or ringleader of the cell, had travelled to Pakistan in December 2004 to learn how to make the bombs using hair bleach at the same time as two of the July 7 attackers.

Security sources have told The Independent they believe Ibrahim, who used his newly obtained British passport to travel to Pakistan, attended the same training camp as Shahzad Tanweer, one of the July 7 bombers, near the Kashmir border. The judge said that although the two cells were separate, he had no doubt they operated in parallel and that their attacks were inspired and controlled by al-Qa'ida.

During sentencing yesterday, he said: "This was a viable, indeed a very nearly successful attempt at mass murder. It was long in the planning and came soon after 7 July - it was designed for maximum impact. The evidence leads me to the firm conclusion that these were not truly isolated events ... They were to an extent co-ordinated and connected in that I have no doubt they were both part of an al-Qa'ida-controlled sequence of incidents."

The sentencing was watched from the public gallery by two members of the public who intervened after Mohammed detonated his device at Oval station. One of the men, Angus Campbell, an off-duty firefighter, was singled out for praise for his bravery. He confronted Mohammed in the train carriage and helped a mother and her child to safety.

The court heard that each of the bombers, who were convicted on Monday at the end of a six-month trial, could have been in no doubt of the outcome of their attack, which would probably have succeeded if the concentration of the chemicals in the devices had been slightly altered.

The judge said: "The family and friends of the dead and the injured; the hundreds, indeed thousands, captured underground in terrifying circumstances; the smoke, the screams of the wounded and dying - this each defendant knew. They planned this, they prepared for it. They had each spent many hours making viable bombs. After 7/7, each defendant knew exactly what the result would be."

The two remaining defendants in the 21 July case face a retrial after the jury failed to reach verdicts. Manfo Kwaku Asiedu, 34, the "fifth bomber" who abandoned his device, and Adel Yahya, 24, who left Britain a month before the bombings, face a new trial for conspiracy to murder.