[3] In an unpublished memoir, Knight recalled that he joined the first of the Fascist Movements in Britain, Rotha Lintorn-Orman's British Fascisti, in 1924, "at the request of the late Sir George Makgill who was then running agents on behalf of Sir Vernon Kell, Director General of the British Security Service, MI5.
Initially, he ran the Section from his flat in Sloane Street but later, he did so for years from 308, Hood House, Dolphin Square in London, again separate from the rest of MI5.
[8] Joan Miller, who was recruited as an agent by Knight and had a close personal relationship with him, remembered that he felt very deeply about the threat of Communism: "his views on this subject, you might say, amounted almost to an obsession.
[12][13] A respected case officer, Knight achieved successes with the infiltration of political groups, leading to the internment and imprisonment of fascists and fascist sympathisers regarded as a threat to the United Kingdom, such as Albert Williams, George Whomack, Anna Wolkoff, Tyler Kent, leading anti-semite, Captain Archibald Maule Ramsay MP, Oswald Mosley, along with communists, such as Percy Glading.
During his career with MI5, Knight found that there was "a very long standing and ill-founded prejudice against the employment of women as agents", a position with which he did not agree.
Agents working under him included Olga Gray (who infiltrated the leadership of the Communist Party of Great Britain), and Joan Miller (who "penetrated the anti-semitic underworld of British Fascism").
Patricia Craig notes that his paper, "The Comintern is not dead", which predicted with great accuracy the developments in Russia's policy with regard to Britain after the war, "was dismissed as 'over-theoretical' by Roger Hollis, and various other Soviet experts considered it unimpressive.
Knight conducted his broadcasting career alongside his work in intelligence, until 1956, when he retired early from MI5, on the grounds of ill health, suffering from angina.
By then he had made over 300 radio broadcasts, had appeared in 40 television programmes and had penned numerous books about natural history and animals.
[23] Knight spent his last years at "The Wing", Josselyns, Midgham, near Reading in Berkshire, where he died from heart failure on 24 January 1968.
Knight's biographer makes this comment about the spymaster's legacy:[17]Perhaps his greatest achievement in MI5 was to help destroy British Fascism during the Second World War ...
Other highlights include his work on the Woolwich Arsenal Spy Ring, his penetration of the Right Club and the prosecution of Tyler Kent and Anna Wolkoff.On the other hand, Henry Hemming's 2017 biography states that Knight was responsible for warning William Joyce in 1939 that he was to be arrested, allowing the latter to move to Germany where he was renowned for his wartime propaganda broadcasts as "Lord Haw-Haw".
[26] In October 2015, a hitherto unpublished 50,000-word manuscript, entitled "The Frightened Face of Nature",[27] written by Knight in 1964, and discovered by Professor John E. Cooper and Simon H. King in Knight's personal filing cabinet, was published in The Guardian, under the headline, "Spectre of destruction": The Lost Manuscript of the Real-Life 'M'.