Four men who came to Britain as refugees from war-torn African nations and were turned by extremist clerics into suicide terrorists face spending the rest of their lives in jail after being convicted of the 21/7 bombing plot yesterday.

Muktar Said Ibrahim, 29, Yassin Omar, 26, Ramzi Mohammed, 25, and Hussein Osman, 28, were found guilty by a jury of conspiracy to murder by detonating rucksack bombs on Tube trains at Oval, Warren Street and Shepherds Bush and on the top deck of a No 26 bus at Shoreditch.

Their suicide mission – which, the court was told, failed only because of a single error by Ibrahim in making the hydrogen peroxide explosives – came a fortnight after the 7/7 attacks that killed 52-passengers on the London transport network.

The six-month trial at Woolwich Crown Court heard that the 21/7 bombs were intended to be “bigger and better” than those that had exploded with devastating effect two weeks earlier.

As the guilty verdicts were read out, Ibrahim, the ringleader of the plot, closed his eyes and bent his head. Omar and Mohammed both stared straight ahead at the judge, while Osman briefly shut his eyes.

Two years ago they had created panic in London, forcing commuters to relive the horrors of 7/7. Yet Tube passengers had confronted their would-be murderers and chased them off the trains.

The 21/7 bombers had radically different profiles from the doctors and medical students arrested last week in connection with attempted car bombings in London and Glasgow.

All four were young refugees from Somalia, Eritrea and Ethiopia who had sought safety in Britain where they received education, were given housing and claimed welfare benefits. But they turned for religious guidance to Abu Hamza al-Masri, the extremist Muslim cleric who preached hatred, intolerance and holy war at the Finsbury Park mosque in North London.

The bombers’ public association with extremism raises difficult questions for the police and intelligence services.

Ibrahim, the plot’s ringleader, had crossed the police and intelligence radar on several occasions in the 14 months before the bombings.

He was photographed by a covert police surveillance team at a jihad training camp in the Lake District in May 2004. Omar, Mohammed and Osman were also present. In August that year, police cameras captured Ibrahim during disturbances outside the Finsbury Park mosque. Despite having a lengthy criminal record for robbery and violence, he was granted a British passport in September 2004.

Three months later Special Branch officers interviewed him for four hours at Heathrow airport as he prepared to fly with two other men to Pakistan. The court heard that his travelling companions died fighting as insurgents in Iraq.

In February 2005 – five months before the bombing attempts – an arrest warrant was issued for Ibrahim when he failed to answer the assault charge. Police wrote to him twice saying: “Come to us before we come to you.” He was not arrested, however, and Ibrahim returned from Pakistan in March 2005 and remained free to plan the 21/7 attacks.

Ibrahim, the jury was told, had been in Pakistan in 2004-05 at the same time as the 7/7 bombers Mohammad Sidique Khan and Shehzad Tanweer. It was admitted two months ago that they had also been caught up in antiterrorist surveillance operations before they carried out their attacks.

Clifford Todd, of the Forensic Explosives Laboratory, told the court that the type of hydrogen peroxide explosive used on 7/7 and 21/7 had not been seen before in Britain.

The court heard that the concentration of the chapatti flour, hydrogen peroxide, nail polish remover and metal shrapnel failed to detonate because the consistency was wrong.

A combination of poor scientific calculation, extremely warm weather and “sheer good luck” meant the bombs failed to go off, it was claimed.

The bombs had a series of flaws: the hydrogen peroxide concentration was not strong enough and the detonator was not powerful enough, Claire McGavigan, a scientist at the laboratory, told the court.

The jury in the case is still deliberating its verdicts against two other defendants, Manfo Kwaku Asiedu and Adel Yahya. Mr Asiedu, 33, abandoned a rucksack bomb in a park on 21/7 while Mr Yayha, who had allegedly purchased hydrogen peroxide, was abroad at the time of the attacks.

Times Recommends

• Third of Muslim students back killings
• Curfew tames feral yobs of Cornwall
• £3,000-a-month drug free abroad