Anthony Blunt, who worked at Buckingham Palace as Surveyor of the Queen’s Pictures, was secretly a Soviet spy during WWII.

The newly-declassified documents include details about some of the UK's most notorious spies.

A World War II-era tailing guide is among declassified records shedding light on spy game in MI5: Official Secrets, at the National Archives.

Despite advances in electronic surveillance, security service MI5 still relies on human ‘watchers’. Government documents reveal what it takes to follow suspects without being detected.

Top secret MI5 files detailing first-hand accounts of confessions of three of Britain's most notorious double agents including Kim Philby and Anthony Blunt who spied for the Soviet Union were released for the first time on Tuesday.