The British Secretary of State for War, John Profumo, resigns in a sex scandal known as the "Profumo affair".

The Profumo affair was a major scandal in twentieth-century British politics. John Profumo, the Secretary of State for War in Harold Macmillan's Conservative government, had an extramarital affair with 19-year-old model Christine Keeler beginning in 1961. Profumo denied the affair in a statement to the House of Commons, but weeks later a police investigation exposed the truth, proving that Profumo had lied to the House of Commons. The scandal severely damaged the credibility of Macmillan's government, and Macmillan resigned as Prime Minister in October 1963, citing ill health. Ultimately, the fallout contributed to the Conservative government's defeat by the Labour Party in the 1964 general election.

When the Profumo affair was first revealed, public interest was heightened by reports that Keeler may have been simultaneously involved with Captain Yevgeny Ivanov, a Soviet naval attach, thereby creating a possible national security risk. Keeler knew both Profumo and Ivanov through her friendship with Stephen Ward, an osteopath and socialite who had taken her under his wing. The exposure of the affair generated rumours of other scandals and drew official attention to the activities of Ward, who was charged with a series of immorality offences. Perceiving himself as a scapegoat for the misdeeds of others, Ward took a fatal overdose during the final stages of his trial, which found him guilty of living off the immoral earnings of Keeler and her friend Mandy Rice-Davies.

An inquiry into the Profumo affair by a senior judge, Lord Denning, assisted by a senior civil servant, TA Critchley, concluded that there had been no breaches of security arising from the Ivanov connection, although Denning's report was later described as superficial and unsatisfactory. Profumo subsequently worked as a volunteer at Toynbee Hall, an East London charitable trust. By 1975 he had been officially rehabilitated, although he did not return to public life. He died, honoured and respected, in 2006. By contrast, Keeler found it difficult to escape the negative image attached to her by press, law, and parliament throughout the scandal. In various, sometimes contradictory accounts, she challenged Denning's conclusions relating to security issues. Ward's conviction has been described by analysts as an act of establishment revenge, rather than serving justice. In January 2014 his case was under review by the Criminal Cases Review Commission, with the possibility of a later reference to the Court of Appeal. Dramatisations of the Profumo affair have been shown on stage and screen.

The Secretary of State for War, commonly called War Secretary, was a secretary of state in the Government of the United Kingdom, which existed from 1794 to 1801 and from 1854 to 1964. The Secretary of State for War headed the War Office and was assisted by a Parliamentary Under-Secretary of State for War, a Parliamentary Private Secretary who was also a Member of Parliament (MP), and a Military Secretary, who was a general.

In the nineteenth century the post was twice held by future prime minister Henry Campbell-Bannerman. At the outset of the First World War, prime minister H. H. Asquith was filling the role, but he quickly appointed Lord Kitchener, who became famous while in this position for Lord Kitchener Wants You. He was replaced by David Lloyd George, who went on to become prime minister. Between the World Wars, the post was held by future prime minister Winston Churchill for two years. In the 1960s, John Profumo was filling this post at the time of the Profumo affair.