Britain’s largest prison has become the scene of a "potentially explosive" stand-off between two rival groups of Muslims, a report from an independent watchdog has warned.

The Independent Monitoring Board (IMB) at Wandsworth jail in South London said that there was a schism among Muslim prisoners over the prison’s newly-appointed imam, with evidence that some inmates were applying pressure on fellow prisoners to "adopt more militant lifestyles and belief systems".

Its annual report said: "There is a schism existing amongst Muslims in the prison about the imam. There have been petitions from two opposing sides on this subject to the governor.

"We are concerned that unless sensitively managed this issue could become even more emotional and potentially explosive."

It added: "The issues surrounding the current imam should be resolved as quickly as possible."

David Jamieson, chairman of the IMB, said: "It is an issue of how the current imam interprets the Koran. "There is a difference of views between the Asian Muslims and the North African and Afro-Caribbean Muslims."

There were also "very worrying" implications of rocketing use of illegal mobile phones by prisoners, the report said, warning that the number of inmates using mobile phones was "widespread and growing".

The study reflected recent press reports that attendance at religious services had increased because inmates were using them as venues for drug dealing and trading in illegal mobile phones.

Board members had raised a series of concerns about a "major influx" of drugs and mobiles in Wandsworth, which holds 1,456 inmates. "We believe it is essential that there are adequate numbers of officers present at all religious services to discourage illegal activities," the study said.

Drugs were "slipping through the net" when new inmates arrived at the jail, especially remand prisoners, while use of passive drugs dogs was "almost non-existent". The report noted that visitors had even asked why more was not being done to tackle the drugs problem.

"Unless there is an effective preventative blanket introduced to curb the use of mobile phones, the situation is likely to get worse and the possible implications for security, drugs usage and bullying are very worrying," the report warned.

"Surely it is time to introduce effective jamming of mobile phones’ use in all prisons?

Last month Anne Owers, Chief Inspector of Prisons, raised concerns about staff attitudes to inmates at Wandsworth, reporting that nearly twice the average number of prisoners had claimed of staff victimisation, with 12 per cent saying they had been hit kicked or assaulted by staff - three times the average of 4 per cent.

A Prison Service spokeswoman said: "Any signs of radicalisation at the prison are firmly dealt with by a pro-active chaplaincy team.

"The recent Eid meal at Wandsworth was attended by 240 prisoners, representing virtually every Muslim prisoner and a number of non-Muslims, during which the imam was personally praised."

She added: "Wandsworth has a good record on both mobile phone and drug finds."

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