Pastor Paul Song describes how he was left in a state of near constant fear

For part-time chaplain Paul Song, Brixton Prison's oak-beamed 19th Century chapel was an oasis amid the hectic clamour of penal life.

But that was before Islamic extremists hijacked his Bible classes. One afternoon three inmates appeared in the chapel, interrupting a discussion on divine grace to loudly acclaim the killers of Lee Rigby, whose murder by jihadis on a South London street shocked the nation.

To the disbelief of Mr Song and his fellow Christians, the interlopers insisted that hacking to death the 25-year-old soldier was justified since, in their eyes, it avenged the killing of Muslims by British troops.

When Mr Song calmly tried to argue back, he was shouted down. Nor was it the only time his classes were to be similarly disrupted.

'To do this in a place of worship was obscene,' he says. 'Some openly spoke in the chapel in support of Islamic State.'

Today, Mr Song tells The Mail on Sunday in chilling detail how extremist Muslim gangs came to dominate his jail: intimidating prisoners into converting to Islam and physically assaulting him over his Christian faith.

And he describes how he was summarily dismissed from the jail over claims – which he strenuously denies – that he called one inmate a 'terrorist'. He was also falsely accused of espousing 'radical' Christianity.

He believes the complaint was orchestrated by imam Mohammed Yusuf Ahmed, who was appointed as the prison head chaplain in 2015 and soon set about upending the multi-faith religious support offered to inmates.

Initially, Mr Song was denied a proper hearing but this newspaper can reveal that an external investigation eventually cleared him a year later and he has been reinstated.

He claims his dismissal after 19 years' service followed a power shift in the South London prison, where a hardline Muslim contingent, feared by officers and inmates alike, were acting with impunity.

In one chilling incident, extremists stormed his gathering in the prison chapel and began loudly praising the jihadis (Michael Adebolajo, left and Michael Adebowale, right) and who hacked soldier Lee Rigby to death in the street

Gangs in the prison praised the killers of Lee Rigby (pictured)

Mr Song believes the days were numbered for him and other Christian volunteers after Mr Ahmed was appointed. Mr Song taught mainstream evangelical courses which proved popular with inmates, but the new imam banned them, saying the material was too 'extreme'.

Describing a climate of fear inside HMP Brixton, Mr Song, who moved to Britain from South Korea 26 years ago, also claimed:

Inmates were forced – in some cases through violence – to convert to Islam for 'protection'

Muslim inmates jeered, pushed and abused him, calling him 'Chinky' and 'Crazy Christian'

He feared for his safety and always tried to ensure he was in view of a CCTV camera

That the imam vowed to change what he called the 'Christian domination' inside prison

He was forced to hold prayer meetings in a cell because the imam stopped him using the prison chapel

Mr Song said: 'I was very upset by what these men said about Lee Rigby that day. They were making a commotion, saying the murder was justified. I tried to calmly reason with them but was shouted down.

'My courses were often disrupted in this way. Two or three would often come to my classes and rant about different things like how the actions of suicide bombers were justified. There was nothing I could do.'

Yet in a grotesque irony, it was the chaplain, not the extremists, who ended up being punished.

Mr Song's time in Brixton came to an abrupt end in August last year when he was suddenly barred from the prison to which he had given 19 years unstinting service

Of all the elements of his astonishing story, it is perhaps the apparent willingness of the prison authorities to readily accept the allegations and dismiss Mr Song without first seeking his version of events, that is the most troubling.

He believes the most cursory examination of the 'evidence' would have found the claims baseless and says he was denied a face-to-face meeting to defend himself. Although common sense eventually prevailed, it is a wonder he now wants to return.

'Some of the inmates spoke with such hatred about Britain, the Government, the military. It was frightening,' Mr Song said.

Mr Song began to feel the pressure soon after imam Mohammed Yusuf Ahmed (pictured) was appointed as head chaplain in 2015

That he became inured to the outbursts is a measure of just how 'crazy the situation became inside Brixton'. He said: 'Gradually, many of the Christian volunteer chaplains were intimidated into leaving until I was one of only a few remaining.'

Before emigrating to Britain, Mr Song, now 49, was a detective in the South Korean capital Seoul. He became a born-again Christian with a 'burning desire' to help those on society's margins, such as the homeless, drug addicts, and prostitutes, and for many years he ran a shelter in a Brixton vicarage.

Prison imam's bizarre attack on Barbies: Brixton jail's Muslim preacher said 'pornographic dolls' were sign of Judgement Day The Brixton prison imam who Paul Song believes was instrumental in forcing him out of the jail once launched a bizarre attack on Barbie dolls. Mohammed Yusuf Ahmed said in 2011: 'Barbie dolls belong to the top shelf. What is the point of a four-year-old girl having a doll that is dressed going to a nightclub? What is the point of a doll that has voluptuous assets? It's a sign of the Day of Judgment.' For eight years, he was a part-time chaplain at Woodhill high-security prison in Milton Keynes, while also general secretary of the Islamic Party of Britain. The party allegedly advocated the death penalty for public displays of homosexuality and wanted to transform Britain into an Islamic state. In 2014, it was reported that Ahmed, who also uses the name Shaykh Yusuf Az-Zahaby belonged to the Islamist organisation Al-Hikma Media where some preachers have advocated killing women who engage in premarital sex. Advertisement

Pastor Paul, as he was known, became a popular, familiar and respected local figure. Outgoing and brimming with enthusiasm, he made friends easily. He is an evangelist but, as he pointed out, so too was Jesus. 'It doesn't make me an extremist,' he laughed. The 43,000 people who signed a petition demanding his reinstatement after his dismissal would agree.

After the Church of England sold off the vicarage-turned-hostel he used to run, he decided to devote more time to voluntary work in Brixton Prison.

Relating to inmates, some of them highly dangerous, came naturally. 'I think my time in the police helped,' he said. His popularity spread and his courses were oversubscribed, attended by up to 80 prisoners.

They met in the large multi-faith chapel, built in the 1850s when embracing Christianity was deemed essential to rehabilitation. 'I was happy that everyone used the chapel and I always got on with people from all religions,' Mr Song recalled. 'In the early days there was never any trouble.'

He turned many inmates' lives around. 'There was one, very dangerous, who sliced open a man from top to bottom and was fond of saying he was going to finish him off when he got out. I helped him find God. He became a new man.'

There were three full-time chaplains – one Catholic, one Muslim and one Anglican, the Reverend Phil Chadder, who led the chaplaincy. But in 2015, Mr Chadder moved on, creating a power vacuum that would later have significant repercussions for Mr Song.

He described the intimidating situation inside the prison at the time: 'Prisoners told me of other inmates who were punched, roughed up, and threatened by Muslim gangsters who told them to convert to Islam for their own protection. They also said that if they refused they would make sure they didn't receive the good quality food, the halal meat, for instance, that was served every Friday.

HMP Brixton, where Mr Song described a culture of fear

'They also tried to convert me. They'd scream in my face, Arabic things such as 'Allahu Akbar' – Allah is greatest. They'd also criticise Christianity, comparing it unfavourably to Islam.

'One day I was walking through a section of a wing housing many of the Muslim prisoners when one of them came at me from behind and hit me hard on the back. They were all laughing calling me a 'Chinky' and 'Crazy Christian'. It was very frightening and, from then on, I was very conscious of walking only where I knew there was CCTV.'

Following imam Mohammed Yusuf Ahmed's appointment, Mr Song's role became more precarious still. Court documents state Mr Song was running the Alpha courses, popular in churches across the country, until 2013. He subsequently created his own course, approved by Mr Chadder. But then 'the imam's discriminatory agenda became clear from the outset,' Mr Song said. 'He began scrutinising the material for each of our courses, saying it was 'too radical' and that the Christian views expressed were 'extreme'.

A Prison Service spokesman said: 'There is absolutely no evidence to support claims relating to extremist behaviour at HMP Brixton' (pictured)

'He paid scant regard to the fact that the courses are mainstream Christian, used by churches throughout the world. He said he wanted to 'change the Christian domination' within the prison.'

Reluctantly, Mr Song agreed to stop running his classes though he continued to work with individual prisoners. 'The imam said I couldn't use the chapel and effectively took control of it so I held a prayer meeting in a large holding cell but the imam got to hear about it and was furious. He is very big, physically intimidating and he kept urging me to just leave. I thought about it but I also thought, why should I give in?'

Following a visit to the jail in January 2017, prisons inspector Peter Clarke found high levels of violence and reported that 'a third of prisoners felt unsafe'. It was also noted that the jail had been without a full-time Anglican chaplain for 18 months. Mr Clarke said one should be recruited 'without delay'.

In August 2017 the imam sent an email to Mr Song warning him not to visit the prison without prior permission or 'you will be walked to the gate'. Mr Song thought there had been a misunderstanding. After all, he had long been so trusted he had his own key.

Mr Song says extremist Muslim gangs came to dominate his jail: intimidating prisoners into converting to Islam and physically assaulting him over his Christian faith

Seeking answers, he went to see the imam. He was told he was no longer welcome and could not appeal the decision.

He then received a letter from Graham Horlock, the prison official in charge of reducing offending, saying he had received allegations that he had called a prisoner a 'terrorist', made references to IS and had threatened the imam. All this Mr Song vehemently denies.

The letter went on to say that the decision to remove him was 'permanent and with immediate effect' – with the ban coming before he had the chance to defend himself.

Mr Song said the imam 'did not elaborate on which of my views he considered extreme, though I had only ever spoken the Bible's message on forgiveness and grace.

'His comments were deeply hurtful, and paid no regard to my unblemished record throughout my two decades of service.'

Before emigrating to Britain, Mr Song, now 49, was a detective in the South Korean capital Seoul

He said he was aware of other Christian groups that went into Brixton and had their courses stopped and this led to Christian volunteers largely being shut out.

Many inmates made witness statements in support of Mr Song. One, Nigel Williams, praised Mr Song's work, saying: 'Hundreds of ex-prisoners have the highest respect and admiration for Paul and would say that his actions changed their lives for the better. The prisoners are devastated by his removal.'

He added that while there was a 'lot of support for Muslims' little was being done for Christians, adding that violent Islamist gangs 'are trying to spread their religion by force' and radicalise inmates.

Another former prisoner, Jeremy Conlon, said in a witness statement: 'The Muslim prisoners created by far the largest gang that ruled the prison by threat of violence. The Muslims offered converts protection. With a shortage of guards this protection became invaluable.'

Those who didn't convert, said Mr Conlon, lived in fear. He said it was impossible to 'speak out about the oppression without facing a genuine risk of being attacked.'

In despair over his situation, Mr Song turned to the Christian Legal Centre, which sought a judicial review of his ban. In May this year, Mr Song agreed to stay the proceedings after an independent investigation was promised.

Led by Sara Pennington, governor of Elmley prison, it said Mr Song should be reinstated, after training for dealing with a 'multi-faith community'. She said HMP Brixton's initial investigation was 'limited' and did not follow due process.

Meanwhile the imam has been suspended over a matter unrelated to Mr Song's case and the prison is now advertising for a new head chaplain. The imam could not be reached for comment.

Andrea William of the Christian Legal Centre, said: 'It is wonderful to see justice done.'

A Prison Service spokesman said: 'There is absolutely no evidence to support claims relating to extremist behaviour at HMP Brixton.'

Mr Song is now planning to restart his courses. 'This has been a very difficult time,' he said. 'Not for a moment did I think that something like this could happen in England.'