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.

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

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.

Avoid false beards, carry plenty of spare change and know what to do when you need to tell a taxi driver "follow that cab!" - these were some of the tips given to rookie MI5 "watchers".

MI5 feared film star Dirk Bogarde could be the target of a KGB gay "entrapment" attempt after it emerged he was on a list of 'six practising British homosexuals' passed to the Russians

The guidance will feature in a new exhibition at the National Archives focusing on the work of the Security Service.

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

Newly declassified files reveal the late Queen's very unexpected reaction to the art historian's shocking secret.