Lee Bradley Brown, 39, of Dagenham was arrested for allegedly physically assaulting a housekeeper at the Burj al Arab Hotel. He died after being held for six days, The Daily Telegraph reported.
The Foreign Office officially notified his family of his death Wednesday. His sister said she had received a call earlier from a fellow prisoner who found her phone number in Brown's passport.
British officials said Consul General Guy Warrington told Dubai Police Chief Dhahi Khalfan Tamim the government expects a "full and open" investigation. The consulate has reportedly been interviewing other prisoners.
Australia and New Zealand have also been pressuring Dubai to guarantee any of their nationals who are in custody there will be safe. Dubai has denied Brown was beaten or subjected to other mistreatment.
"First thing I knew he was on holiday in Dubai -- next thing I know he's dead -- part of me has died with him," his mother, Doris Brown, said. "If anybody didn't deserve that kind of treatment it was him. He never did harm to anyone."
Brown, a self-employed maintenance man, was staying at a hotel where rooms cost about $1,600 a night.