Victor Rothschild, 3rd Baron Rothschild

In Who Paid the Piper? (1999), an account of CIA propaganda during the Cold War, author Frances Stonor Saunders alleges that Rothschild channelled funds to Encounter, an intellectual magazine founded in 1953 to support the "non-Stalinist left" to advance US foreign policy goals.

In his 1994 book The Fifth Man, Australian author Roland Perry asserted that in 1993, after the dissolution of the Soviet Union, six retired KGB colonels, including Yuri Modin, the spy ring's handler, alleged Rothschild was the so-called "Fifth Man": "Rothschild was the key to most of the Cambridge ring's penetration of British intelligence. "He had the contacts", Modin noted. "He was able to introduce Burgess, Blunt and others to important figures in Intelligence such as Stewart Menzies, Dick White and Robert Vansittart in the Foreign Office ... who controlled MI6." However this suggestion is rebutted by other researchers; commentator Sheila Kerr pointed out that as soon as the book came out, Modin denied Perry's version of their discussions (having already stated that the fifth man was Cairncross), and concluded that "Perry's case against Rothschild is unconvincing because of dubious sources and slack methods". Noel Annan, who was criticised by the author Perry for a negative view of the latter's book and claims, writes: "Amid clouds of misstatements he [Perry] relies almost wholly on insinuation and bluster. ... when Andrew Boyle published his book and exposed Blunt, why did Margaret Thatcher acknowledge in the House of Commons the truth about Blunt, but later, in the case of Rothschild, clear him? Mr. Perry is saying she lied to the House. He tries to make much of her curt statement, "I am advised that we have no evidence that he was ever a Soviet spy." It is the only official reply she could have made. In MI5 jargon there was "No Trace" against his name". Christopher Andrew and Vasili Mitrokhin, in The Mitrokhin Archives, make no mention of Rothschild as a Soviet agent and instead identify John Cairncross as the Fifth Man.

He appears several times in the book Spycatcher, which he hoped would clear the air over suspicions about his wartime role and the possibility he was involved in the Cambridge spy ring. In early 1987 Tam Dalyell MP used parliamentary privilege to suggest Rothschild should be prosecuted for a chain of events he had "set in train, with Peter Wright and Harry Chapman Pincher" which had led to a "breach of confidence in relation to information on matters of state security given to authors".

Despite being an opposition Labour party peer, in 1987, during the Thatcher Government, Victor played a role in the sacking of Director-General of the BBC Alasdair Milne, who had backed the programmes Secret Society, Real Lives, and Panorama: 'Maggie's Militant Tendency' which had angered the Thatcher government. Marmaduke Hussey, who was Chairman of the BBC Board of Governors at the time, implied Rothschild initiated the Milne sacking in his autobiography Chance Governs All.

Rothschild took the step of publishing a letter in British newspapers on 3 December 1986 to state "I am not, and never have been, a Soviet agent".

In 1982 he published An Enquiry into the Social Science Research Council at the behest of Sir Keith Joseph, a Conservative minister and mentor of Margaret Thatcher.

In the 1980s, Rothschild joined the family bank as chairman in an effort to quell the feuding between factions led by Evelyn Rothschild and Victor's son, Jacob Rothschild. In this he was unsuccessful as Jacob resigned from the bank to found J. Rothschild Assurance Group (a separate entity, now St. James's Place plc).

Rothschild published two volumes of memoirs, Meditations of a Broomstick (1977) and Random Variables (1984).

Rothschild was head of the Central Policy Review Staff from 1971 to 1974 (known popularly as "The Think Tank") a staff which researched policy specifically for the Government until Margaret Thatcher abolished it.

In 1971 Rothschild was awarded an honorary degree from Tel Aviv University for ''the advancement of science, education and the economy of Israel''. It was followed in 1975 by an honorary degree from Jerusalem's Hebrew University. The annual "Victor Rothschild Memorial Symposia" is named after Rothschild.

When Anthony Blunt was unmasked as a member of the Cambridge Spy ring in 1964, Rothschild was questioned by Special Branch (though Blunt was not publicly identified as a Soviet agent until 1979 in the House of Commons by Prime Minister Margaret Thatcher). Rothschild was cleared, and continued working on projects for the British government.

Flora Solomon claims in her autobiography that in August 1962, during a reception at the Weizmann Institute, she told Rothschild that she thought that Tomás Harris and Kim Philby were Soviet spies.

After the war, he joined the zoology department at Cambridge University from 1950 to 1970. He served as chairman of the Agricultural Research Council from 1948 to 1958 and as worldwide head of research at Royal Dutch/Shell from 1963 to 1970.

In 1946, he married Teresa Georgina Mayor (1915–1996), who had worked as his assistant at MI5. Mayor's maternal grandfather was Robert John Grote Mayor, the brother of English novelist F. M. Mayor and a greatnephew of philosopher and clergyman John Grote. Her maternal grandmother, Katherine Beatrice Meinertzhagen, was the sister of soldier Richard Meinertzhagen and the niece of author Beatrice Webb. They had four children:

Rothschild inherited his title at the age of 26 following the death of his uncle Walter Rothschild, 2nd Baron Rothschild on 27 August 1937. He sat as a Labour Party peer in the House of Lords, but spoke only twice there during his life (both speeches were in 1946, one about the pasteurization of milk, and another about the situation in Palestine).

At Trinity College, Cambridge, he read physiology, French, and English. Later he worked in the Zoology Department before gaining a PhD in 1935. He played first-class cricket for the University and Northamptonshire. At Cambridge he was known for his playboy lifestyle, driving a Bugatti and collecting art and rare books.

In 1933, Rothschild gave Blunt £100 to purchase "Eliezer and Rebecca" by Nicolas Poussin. The painting was sold by Blunt's executors in 1985 for £100,000 and is now in the Fitzwilliam Museum.

In 1933, he married Barbara Judith Hutchinson (1911-1989). They had three children.

Nathaniel Mayer Victor Rothschild, 3rd Baron Rothschild GBE, GM, FRS (31 October 1910 – 20 March 1990) was a British banker, scientist, intelligence officer during World War II, and later a senior executive with Royal Dutch Shell and N M Rothschild & Sons, and an advisor to the Edward Heath and Margaret Thatcher governments of the UK. He was a member of the prominent Rothschild family.