It's believed Philby learnt of this MI5 investigation and as the intelligence service prepared to interrogate Maclean, Philby sent Burgess to tell him he was in danger. Second World War intelligence – AIR 24– these are RAF Operations Record Books and they contain hundreds of intelligence reports – search simply for ‘intelligence’

In October 1950 Kim Philby warned Guy Burgess and Donald Maclean that they were being investigated by MI5. Burgess returned to London and in May 1951 he defected with Maclean to the Soviet Union. This created serious problems for Liddell as Burgess was a close friend and they were often seen together at parties, clubs and the opera. Liddell had also been seen drinking with other suspects Philby and Anthony Blunt in a pub in Chelsea. Mentions in Despatches" (PDF). Supplement to the London Gazette. 12 July 1920. p.7423. Archived from the original on 21 April 2016 . Retrieved 29 October 2014. Official intelligence histories of the First World War written by senior Government Code and Cypher School members of staff in HW 7 Signals intelligence –that is intelligence gathered by the interception of electronic signals as well as other means of communication –is, today, handled by the Government Communication Headquarters (GCHQ).West, Nigel (2008). Woronoff, Jon (ed.). Historical Dictionaries of World War II Intelligence. 1, British Intelligence. Lanham, Maryland: Scarecrow Press. p.9. ISBN 9780810864214. a b c "Kathleen Maria Margaret Sissmore". Ancestry. Ancestry Europe sari. Archived from the original on 12 November 2015 . Retrieved 29 October 2014. Every now and again the National Archive at Kew gives us a gem, a rare glimpse into our nation's recent past and today promises to be one of those days.

The British eventually agreed to the war crimes trials despite the misgivings of some senior government officials who believed the decision to prosecute the surviving Nazi leadership for waging a war of aggression would set a dangerous precedent. They also feared the prosecutions would be on a par with the high-profile show trials in Stalin's Russia. Liddell would never again marry. He soon abandoned the upscale London home he shared with Calypso for a more modest flat. He became more reclusive as time went on devoting much of his energy to MI5 work.

Guy Liddell Diaries

Liddell kept an almost daily diary containing details of his work at MI5 throughout the Second World War, dictated to, typed up and indexed by his secretary, Margot Huggins. Military historian Rupert Allason, writing under the pen name of Nigel West, has edited Liddell's wartime diaries for publication in two volumes.