British spies are deliberately not interviewing British Islamic State suspects in Syria partly because of fears any contact could strengthen the detainees’ case for returning to the UK, The Sunday Telegraph has learned.

The government is worried that any encounter between MI6 officers and British Isil suspects risks giving the detainees a legal foothold which they could exploit to come back to Britain, UK officials said.

Britain’s intelligence agencies have also been dogged by years of lawsuits over their role in the treatment of suspected jihadists abroad, leading MI6 officers to maintain “a strategic distance” from UK detainees in Syria.

The result is that high-profile British suspects including the two surviving members of ‘The Beatles’ - the cell responsible for torturing and murdering Western hostages on camera - have not been debriefed by UK intelligence officers.

The UK is instead relying on the CIA or US special forces to speak to the Isil suspects and pass the information back to Britain. British intelligence is understood to be feeding questions directly to the Americans, in some cases getting them to ask detailed questions about UK cities.

Several British detainees said they had been interviewed by the US but not by the UK.