When transcribers went back over a conversation the men had held in the car, they were picked up discussing killing Gary Smith and praising Allah as they drove from the scene after attacking him.

Akmol Hussein, 27, Sheikh Rashid, 27, Azad Hussain, 26, and Simon Alam, 19, all admitted causing grievous bodily harm with intent after ambushing Mr Smith outside his school.

Azad Hussain, left to right, Akmol Hussein, Sheikh Rashid, and Simon Alam all admitted causing grievous bodily harm with intent after ambushing Gary Smith, left, outside his school

Akmol Hussein was heard setting out the plan to attack Mr Smith, head of religious education at Central Foundation Girls’ School in Bow, east London, saying in a Bangladeshi dialect: ‘This is the dog we want to hit, to strike, to kill.’

‘He’s mocking Islam and he’s putting doubts in people’s minds…How can somebody take a job to teach Islam when they’re not even a Muslim themselves?’ he added.

Mr Smith, 37, had been head of religious studies at the school for eight years and was described as an able, enthusiastic and popular teacher.

He followed the national curriculum by teaching his pupils all six of the main religions along with ethical issues such as abortion and euthanasia and the role of women.

After the attack, the teacher was left with a four inch slash across his face from the corner of his mouth to his right ear and suffered a fractured skull and shattered jaw.

He underwent an operation to repair leg and facial wounds and nerve damage and did not regain consciousness until two days later.

Jailing the gang at Snaresbrook Crown Court, Judge Hand said they had “literally smashed Mr Smith’s face in.”

He said the motivation for the attack was solely down to the victim’s religious beliefs. He told them: “You believed there was a higher authority to which you were responsible and that authority dictated you must attack Mr Smith.

The judge added: ‘Only time will tell whether you will ever have a different belief but, at present, I believe that if you think that the people around you are guilty of posing a threat or insult to the way in which God intends the world to be and in which God intends people to live you would not hesitate in acting again in the way you have acted in this case.’

Judge Hand handed Akmol Hussein, a self-employed builder, and Azad Hussain, a finance worker, indeterminate sentences for public protection and ordered they serve at least five years before they can be released.

Simon Alam, an engineering student, was ordered to serve at least five years in a Young Offenders’ Institute and Sheikh Rashid, a bus driver, was jailed for at least four years.

A fifth man, Bangladesh-born Badruzzuha Uddin, 24, who helped the men by hiding blood-stained clothing, was jailed for two years.

Uddin and Alam, born in Germany, may now face deportation.

The gang made at least two aborted attempts to target Mr Smith in the days before the attack, finally catching up with him as he made his way on foot along Burdett Road in Mile End at 8am on July 12 last year.

Moments before the attack, as the men pulled on gloves, Azad Hussein could be heard saying: ‘Does everyone remember the drill? One time, bang, bang, bang, bang.’

The recording was then silent for ten minutes while the attack took place.

In the course of the attack Mr Smith was attacked with a knife, a metal rod and a brick and was hit in the stomach, and kicked in the head and face as he lay on the ground.

After the attack, the four men, pumped up on adrenaline, returned to Akmol Hussein’s Ford Focus where they were heard boasting about the attack, praising Allah and listening to Jihadi music.

Akmol Hussain said: ‘Praise to Allah. At that time nobody was there…Bruv, I don’t care about prison as long as I’m doing it for the deen [religion] of Allah…you know what, he’s not going to get up”

Arabic chanting in the background included the lyrics: ‘If we are killed, then our Lord’s heavens are for us. If we are victorious, it is the inevitable promise’.

Traces of Mr Smith’s blood were found in Uddin’s car and the attackers’ blood-soaked clothing was found in a garage where Uddin worked as a mechanic. DNA testing showed the blood was Mr Smith’s and the clothing had been worn by Akmol Hussein and Simon Alam.

When they were first detained the five men either refused to comment or denied their involvement in the attack but they were rearrested in August after police transcribed and translated some of the material recorded in Akmol Hussein’s car.

Despite suffering depression, anxiety and horrific physical injuries, Mr Smith, a former martial arts enthusiast, has returned to his job.

Days after the assault, he said: ‘I’m determined to be back at work,” but added: “I wouldn’t want anybody else to suffer what I went through. I survived but somebody else might not.’

Superintendent Colin Morgan of Scotland Yard said: “I know that the community of east London has been shocked by this vicious assault on a valued and highly respected teacher.

“This was an unprovoked and premeditated attack by a group of men who were carrying weapons. Mr Smith was struck without warning, and was subjected to an appalling level of violence with no opportunity to defend himself.”