Most of the Pakistani men arrested last week in an anti-terrorist operation will be deported rather than charged, senior counter-terrorism sources told The Times last night.

Officials in London and Islamabad said that Britain had begun seeking assurances about how the men would be treated if they were returned to Pakistan. “The British wanted to be reassured that if some of these men were deported they would not face torture,” an informed source in Pakistan said.

One of the 12 men detained, an 18-year-old, has been freed from anti-terrorist detention and is in the custody of immigration officials.

Investigators are concerned that they have not found any firm evidence linking the men to terrorist attack plans. A source close to the inquiry said: “There is already talk of coming up empty-handed and there is terrible infighting between the different forces involved.”

Operation Pathway, the codename for the inquiry, has already led to the resignation of Britain’s most senior anti-terrorist officer, Bob Quick, after he accidentally revealed details of the arrest plans to photographers in Downing Street. If it results in deportations rather than charges, it will also embarrass the Prime Minister, who said that the police were dealing with “a very big terrorist plot” and had criticised Pakistan for not doing more to tackle Islamist terrorism.

The latest discussions between London and Islamabad were disclosed as news emerged from Pakistan that its anti-terrorist agencies had been holding a British convert to Islam for two weeks. James McLintock, 44, was detained in Peshawar, from where many of the men arrested in Britain come, and is being questioned about helping British Muslim militants to make contacts in Pakistan.

Pakistani and British officials said that the arrest of Mr McLintock, from Dundee, was not linked to the continuing terrorism investigation in Britain. The last time he came to the attention of the British authorities, however, was in late 2003 when he was questioned by anti-terrorist police in Manchester, the city at the heart of the plot allegations.

The family of a man studying at Liverpool John Moores University said they believed that their son had been arrested and appealed for his release. Relatives of Mohammad Ramzan, from Dera in Pakistan, said that they had been unable to contact him since last week. Haji Hazrat Ali, his father, told Associated Press that Mr Ramzan, 25, travelled to Britain in 2006 and was studying for an MBA. Mr Ali said: “He is a very humble, gentle boy and always concentrates on his studies. I firmly believe he simply cannot be involved in any negative activity.”

The operation in Britain has been running covertly for several weeks and went public last Wednesday, within hours of Mr Quick’s blunder, with dramatic daylight raids in Manchester, Liverpool and Clitheroe, Lancashire. The remaining 11 detainees, 10 of whom are believed to be Pakistani nationals visiting Britain on student visas, are being questioned at police stations across the North of England.

Detectives have been granted a further seven days to detain the suspects, who range in age from 22 to 41. They can be questioned for a maximum of 28 days before they have to be charged or released.

The investigation is a joint operation between the North-West Counter-terrorism Unit, Scotland Yard’s counter-terrorism command and MI5, and involved Merseyside and Lancashire constabularies. The involvement of so many forces is said to have led to infighting and confusion over the command and direction of the inquiry.

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