During interrogation by the Fluency Committee in the 1960s Ellis had, in the words of West, allegedly "made a limited confession, admitting his links to the Germans and claiming to have been kept impossibly short of money, but denying that he had ever succumbed to pressure from the Soviets, although he acknowledged it was likely they had learned of his treachery".

[4] Prime Minister Margaret Thatcher's refusal to confirm or deny Pincher's allegation caused distress to the Ellis family[5][6] and his daughter, Ann Salwey, returned her father's medals to the British Government in protest.

Ellis may have fed his White Russian contacts in Paris with information of a kind in the hope of using them both as a means of finding out what the Abwehr were interested in, and of creating a degree of confidence which could then be turned to advantage.

According to his biographer, Jesse Fink, Ellis ‘entered the actual "theatre of war" on 19 October 1916 in France, where he fought in the First Battle of the Somme commanded by Douglas Haig (which ended on 13 November 1916), got promoted to lance corporal (second-in-command of a section), [and] was repeatedly maimed.

After convalescing in a British hospital and further training in Troon, Scotland, Ellis joined the 4th Battalion Middlesex Regiment, was commissioned as a junior officer in September 1917,[14] and later promoted to captain.

Writes Fink: 'The original campaign to thwart German and Turkish incursions in Central Asia and India was two-pronged: Major General Lionel Dunsterville’s "Dunsterforce" led a British Indian Army brigade in Baku, capital of the newly formed and oil-rich Azerbaijan, and Major General Wilfrid Malleson, assistant quartermaster-general for intelligence, focused on the area from Meshed in Persia to Merv in Transcaspia: a distance of about 400 kilometres.

Ellis fundamentally disagreed with claims by the Socialist Revolutionary journalist Vadim Chaikin that British officers were responsible for the deaths of the Commissars, pointing out that it had been a triumph for Soviet propaganda.

Keith Jeffery wrote that the 22000 Organisation's main tasks 'were the penetration of Germany and Italy... agents were recruited mostly from the business, journalistic and academic world'.

[27] In June 1940 Ellis was appointed deputy head to William Stephenson at British Security Co-ordination in New York, after the two men were introduced in 1938 in London by Sir Ralph Glyn.

And that led to his being asked if he was going to America... if he would do what he could to reestablish a link between security authorities here and the FBI.’[30] Agents recruited to BSC included Ian Fleming, Roald Dahl, Noël Coward and H. Montgomery Hyde.

[31] Here, in the period before Pearl Harbor, Ellis briefed J. Edgar Hoover in counter-espionage techniques and provided the blueprint from which William J. Donovan was able to set up Coordinator of Information and the Office of Strategic Services.

In September 1944 he returned home to England but visited Washington, DC, in 1946 for talks with General John Magruder of Strategic Services Unit, the successor to OSS.

Colonel Ellis’s assistance during the above period of experimentation and growth was invaluable particularly in the absence of any American precedent in the initiation and operation of a clandestine intelligence organisation.

‘Throughout the above period Colonel Ellis was a daily visitor to the COI (OSS) offices, where his helpfulness and advice were generously made available to the Secret Intelligence Branch.

His enthusiastic interest, superior foresight and diplomacy were responsible in large measure for the success of highly important operations and to furtherance of Anglo-American cooperation.’[37] At MI6, Ellis was promoted to Chief Controller Pacific (Far East and the Americas), making him, in the words of Fink, 'effectively one of the most powerful intelligence agents in the world, with responsibility for North and South America and those regional hotbeds of communism, East Asia and South-East Asia'.

[40] He continued visiting Australia throughout the 1950s, '60s and '70s, primarily working on books, pamphlets and journal articles, with two unpublished manuscripts (Anglo-American Collaboration in Intelligence and Security: Notes for Documentation and The Two Bills: Mission Accomplished) forming the basis for H. Montgomery Hyde's The Quiet Canadian (1962) and William Stevenson's A Man Called Intrepid (1976).

Following the defection of Kim Philby to the Soviet Union in 1963, Ellis was the subject of an internal MI5-MI6 investigation headed by Peter Wright's Fluency Committee and underwent interrogation in London, during which he allegedly made a confession that he had supplied information to the Nazis prior to World War II.

[44] Dorril wrote in his book MI6: Fifty Years of Special Operations (2000): ‘There is a suspicion that [Ellis] was later made a scapegoat in order to hide a more disturbing fact, namely that he had been trading information with the Germans on the orders of [MI6 chief] Stewart Menzies... until the end of 1938, MI6 believed that Hitler’s ambitions lay in the East, and that he was “devoting special attention to the eastward drive, to securing control of the exploitable riches of the south, and possibly more, of Russia”.

‘Some of the intelligence that reached the Cabinet may have originated with Ellis, who knew that Admiral Wilhelm Canaris, chief of the Abwehr, had secret plans to use the White Russians in operations in Ukraine and southern Russia.

In the meantime, MI6 was still engaged in plans to thwart Soviet expansionist claims and to deny the Germans access to oil for its war machine.’[45] Ellis is the subject of British-Australian author Jesse Fink's biography The Eagle in the Mirror, which was released in August 2023 in Australia and the United Kingdom.

He was another victim of the Cold War, when hysteria and fear overtook sense and reason, when paranoid intelligence agencies on both sides of the Atlantic were utterly convinced there were other Philbys to be uncovered, so long as they looked somewhere in that wilderness of mirrors.

'There is no transcript, just Peter Wright’s account (as relayed under his own name in Spycatcher and preceded by Pincher’s telling of the story in Their Trade is Treachery and Too Secret Too Long)... so, without irrefutable proof of treason and judged on the breadth of his career, Ellis should be remembered not as a traitor but as one of the great intelligence officers of the 20th century whose character, loyalty, doggedness, reliability and vision marked him out as someone truly significant.

"[48] In a review of the book, Pat Sheil of The Sydney Morning Herald writes 'the point of Fink's work... is to convincingly demolish various attacks on Ellis's reputation, especially the self-serving accusations of treacherous dealings, first with the Nazis and then the Soviet Union, made by a phalanx of bitter, or simply gullible, “insiders”.

'Fink's bile is directed, though not exclusively – his blunderbuss peppers a host of dubious characters – at ex-MI6 spook Peter Wright... [and] Pincher, one of Ellis's most libellous accusers, for blatantly conspiratorial malarkey.