Prime minister David Cameron has expressed his concern over allegations three British men were tortured by police in Dubai after they were arrested on drug charges.
Grant Cameron and Suneet Jeerh, both 25, and Karl Williams, 26, are on trial accused of having a quantity of a synthetic cannabis known as "spice" in their car while on holiday in July last year.
The men, all from London, claim they signed documents in Arabic - a language none of them understands - following their arrests after they were threatened with guns to their heads, the human rights charity Reprieve said.
Williams also reported having electric shocks administered to his testicles during the ordeal, the charity added.
The men have denied charges of "consumption and possession with intent to distribute" and are expected to learn their fate tomorrow when a Dubai judge delivers his verdicts in the trial.
In a letter to Reprieve, the prime minister has said he will use a state visit by the United Arab Emirates (UAE) president in the coming week to raise his concerns about the case.
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 Cameron, Williams and Jeerh and their families."
The men appeared at their first trial hearing in February after spending seven months in custody.
In a draft witness statement provided to Reprieve lawyer Marc Calcutt, Williams described having a towel put on his face by police and having electric shocks on his testicles.
The torture, which the police deny, took place in the desert, it was claimed, where the men were initially taken after their arrest, and subsequently in hotel rooms.
Cameron's mother Tracy said her son's ordeal had been "absolutely awful" but he remained in "good spirits" ahead of the court hearing.
Ms Cameron told the Press Association: "I'm trying to remain strong for my son. We're hopeful this awful situation will be over soon.
"Grant had only been in the country for four days when he was arrested. For 45 minutes they were Tasered, beaten around the head and handcuffed before they were taken back to the hotel where Grant was staying.
"They were put in separate rooms and had guns held to their heads. They were told they would be killed and told they would never see their families again. Grant feigned being diabetic which seemed to calm things down a bit."
Ms Cameron said she has been told by lawyers that her son could be found guilty of at least one of the charges, which may result in a jail sentence of 15 years or longer.
The Foreign and Commonwealth Office (FCO) has called for a full, independent and impartial inquiry into the torture allegations and has raised them with "very senior officials" in the UAE.
Ministers will also express "concerns" about aspects of the UAE investigation into the torture claims during the state visit of President Sheikh Khalifa next week, the Foreign Office added.
A spokeswoman said: "The FCO takes all allegations of mistreatment and torture extremely seriously, and acts with a sense of urgency in all cases.
"We have been providing consular assistance to three British nationals detained in the UAE since July 2012, and are aware of their allegations of mistreatment.
"We have raised, and continue to raise, these allegations at the most senior levels in person and through diplomatic channels, including through ministers.
"We requested a full, impartial and independent investigation into the allegations, and have now received some details of a UAE investigation.
"However, we are concerned about aspects of this and are formally raising these with the Emirati authorities. Ministers will also be raising our concerns during the state visit.
"It would not be appropriate to pre-empt the court judgment on April 29.
"Consular staff have recorded what the detainees told them and their observations, but they are not able to collect formal evidence as they are not qualified to do so.
"We are therefore working closely with Reprieve to find independent experts who can provide assistance."
Cameron and Williams are both from Wanstead, in north-east London, while Jeerh is from Ilford, east London.
The UAE embassy in London refused to comment when contacted today.