Britain will use a state visit by the UAE president this week to raise the case of three Britons who claim they were tortured after being arrested on drugs charges in Dubai, officials said on Sunday.
The news came as the mother of one of the men, Grant Cameron, described their "terrifying ordeal" following their arrest last July, when she said they were beaten and given electric shocks.
Tracy Cameron told the BBC that one of her son's friends, Karl Williams, "was laid out on the bed, his trousers were stripped down and electric shocks were administered to his testicles while he was blindfolded".
She said: "I believe all boys had guns held to their head -- they were told they were going to die.
"Grant sustained electric shocks to his torso and I believe Suneet (Jeerth, the third man) had shocks administered to him to the back of his head and his back."
Authorities in the United Arab Emirates have dismissed the allegations, saying an internal investigation found them to be "baseless".
But the British government is pushing for an independent investigation into the claims, which it says it takes "extremely seriously".
"We have raised, and continue to raise, these allegations at the most senior levels in person and through diplomatic channels, including through ministers," a Foreign Office spokesman said.
"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" by Sheikh Khalifa bin Zayed al-Nahayan, president of the Gulf emirate, which begins on Tuesday, the spokesman said.
The president will stay overnight at Windsor Castle as a guest of Queen Elizabeth II, and will also meet with Prime Minister David Cameron.
The case of the three Britons has been taken up by campaign groups including Human Rights Watch and Amnesty International, who also want London to press Sheikh Khalifa on the treatment of dissidents.
Tracy Cameron said that when her son had informed her about his treatment in a phone call, she felt "beside myself, sheer horror, terror, just complete and utter meltdown really".
"Your son being arrested so far away from home is challenge enough to deal with but, once he told us how he'd been treated, I can only describe it as something from a horror story," she said.