A triple murderer whose prison conditions have raised concerns of torture within the United Nations has reportedly been transferred to another jail.

Along with his brother Miran, Kevan Thakrar – of Lomond Way in Stevenage – was jailed in 2008 for killing three men over a drug deal, and attempting to kill two women.

Keith Cowell, 52, his son Matthew, 17, and Tony Dulieu, 33, were lined up and shot in Bishop’s Stortford in 2007.

Matthew’s girlfriend and a second woman were stabbed after the ammunition ran out.

Kevan is serving a minimum 35-year jail term, but has always maintained he was wrongly convicted. He was found guilty under joint enterprise – a law which has been used against people in gang-related cases if defendants could have foreseen violent acts by their associates.

Campaign group Justice for Kevan Thakrar says he has been transferred to HMP Belmarsh, but are concerned he remains in segregation.

Earlier this year, UN human rights expert Nils Melzer said Kevan has been kept in close supervision centres - which hold about 60 men considered the most dangerous in prison - for the past 11 years.

He said: "He is alone in a cell for more than 22 hours a day, is not permitted to participate in regular prison activities, receives food through a hatch, and does not even have a privacy screen when using the toilet.

“When used for more than 15 consecutive days, these conditions of detention amount to torture or other cruel, inhuman or degrading treatment or punishment, and are neither legitimate nor lawful.

"Both in this individual case and in terms of general policy, we are concerned at the reported use of prolonged or indefinite solitary confinement in CSCs."

The government said it cannot comment on individuals, but "does not agree with the characterisation of the location of prisoners in CSCs as comparable to solitary confinement and rejects the suggestion a prisoner would be located within a CSC unit in an act of retribution by the prison service.

"All prisoners in CSC units are provided with a safe, decent and healthy regime, appropriate to their assessed risk, which includes meaningful human contact and access to rehabilitative and risk reduction work."