MI5

Mr Donaldson, who had worked for Sinn Féin, was shot dead in Donegal in 2006, months after admitting his role as a police and MI5 agent for 20 years.

Mr Donaldson was shot dead in Donegal in 2006, months after admitting his role as a police and MI5 agent for 20 years.

Asked about the Bafta-nominated series Slow Horses, which focuses on intelligence agents who have been discarded by MI5, Lowden talked about being trained in spycraft.

The documents also reveal details of Andrew's "communication channel" with China's President Xi Jinping - including sending an annual birthday letter - and how MI5 intervened to warn against Andrew having contact with the alleged spy.

A battered leather briefcase left behind by Guy Burgess when he fled to Moscow in 1951 is among 20 objects from MI5's archives to go on display for the first time from Saturday.