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.

Rookie wartime MI5 "watchers" were advised they needed to be prepared to offer a big tip if they had to tell a taxi driver to "follow that cab" when pursuing a suspect, newly declassified documents reveal.

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.

That was the advice issued to rookie MI5 “watchers” whose job it was ... focusing on the work of M15 due to open at the National Archives in Kew, west London, in the spring.

MI5 reveals confessions of three members of infamous Cambridge Five spy ring as tranche of documents released into National Archives

Recently released MI5 files reveal confessions from Britain's notorious double agents, including Kim Philby and Anthony Blunt, who spied for the Soviets. These declassified documents, made public by the National Archives,

The guidance is contained in a booklet for recruits during World War Two, which will go on display at the National Archives in Kew, west London Rookie wartime MI5 "watchers" were advised they ...

Five Cambridge University graduates served as double agents, leaking highly classified information to the Soviet Union

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

The manual gives instructions on preferred appearances, disguises and how to follow targets – but warns against fake moustaches