Three British men have been jailed for four years each for possession of drugs in Dubai amid claims that they were tortured by police.

Grant Cameron and Suneet Jeerh, both 25, and Karl Williams, 26, all from London, were convicted of possessing a quantity of a synthetic cannabis after being arrested in July last year while on holiday.

The men claim they signed documents in Arabic - a language none of them understands - following their arrests after they were threatened with guns to their heads. Mr Williams also reported having electric shocks administered to his testicles.

Pressure group Reprieve, which campaigns on behalf of prisoners, said the men should be granted clemency and their torture allegations should be thoroughly investigated.

Reprieve investigator Kate Higham said: "The central fact of this case remains that these men were tortured by police, but there has been no proper investigation into their abuse. The only reasonable course of action for the UAE authorities now is to grant these men clemency, release them and allow them to return home to their families. David Cameron must push for this when UAE President Sheikh Khalifa arrives on a state visit tomorrow. It also remains essential that the UAE conduct an impartial investigation into these men's torture and ensure it is never allowed to happen again."

The Prime Minister has already expressed concern over the allegations and said he will raise them with the president.

In a letter to Reprieve, Mr Cameron wrote: "The UK Government takes all allegations of mistreatment very seriously. We continue to press for evidence for a full, impartial and independent investigation into the allegations. The absence of an independent medical examination remains a concern."

He continued: "During the state visit of His Highness Sheikh Khalifa bin Zayed Al Nahyan there will be opportunities to raise a wide range of issues including concerns about this and other consular cases. We continue to request these cases are fully and independently investigated. I appreciate this must be an extremely difficult time for Mr Cameron, Mr Williams and Mr Jeerh and their families."

Speaking after her son was jailed, Mr Cameron's mother Tracy said she believed he would be home by the end of the year and could even be pardoned within the next few months.

She told BBC Breakfast: "Grant has always pleaded not guilty and his evidence has been pretty consistent throughout from the moment his initial first statement was taken. We have to bear in mind that all three boys were forced to sign documents in Arabic, the information is pretty inconsistent that the UAE authorities showed as evidence in the courtroom... I am very positive that my son will be home with his family by the end of the year at the very latest."