In British politics, the "Night of the Long Knives" was a major Cabinet reshuffle that took place on 13 July 1962. Prime Minister Harold Macmillan dismissed seven members of his Cabinet, one-third of the total. The speed and scale of the reshuffle caused it to be associated by its critics with the 1934 Night of the Long Knives in Nazi Germany.

The reshuffle took place against a backdrop of declining Conservative popularity in Britain. Conservative candidates fared poorly in several by-elections, losing ground to Liberal candidates. Concerned that traditional Conservative voters were expressing their disapproval with the government's economic policies by switching to the Liberals, Harold Macmillan planned to replace his Chancellor of the Exchequer, Selwyn Lloyd, with Reginald Maudling. Lloyd had already clashed with Macmillan over his economic strategies, and Maudling was considered to be more amenable to the economic policies Macmillan wished to implement. The reshuffle was also an attempt to reinvigorate the party, bringing in younger and more dynamic figures and replacing some of the older and less capable ministers. After discussions with Conservative Party chairman Iain Macleod and Home Secretary Rab Butler, a reshuffle was planned for autumn 1962.

Macmillan was overtaken by events when Butler leaked the details of the reshuffle to press baron Lord Rothermere over lunch on 11 July. The newspapers reported the impending changes on 12 July, and Macmillan made the decision to press ahead with the reshuffle at once. Lloyd was called to a meeting that evening and dismissed. The remaining six were informed the following day, 13 July. Macmillan faced sharp criticism over the scale of the changes, and his political opponents both within the Conservative Party and in the Opposition characterised him as ruthless and opportunistic. Despite an initial sharp drop in his approval ratings, opinion eventually swung back in his favour and the Party recovered. Macmillan regretted the way the reshuffle was carried out, and was particularly concerned about his treatment of Lloyd, who was a loyal confidant. Despite the dramatic changes in the Cabinet, the Conservatives were rocked by a series of scandals in 1963 and Macmillan retired in October of that year, citing ill health. He was replaced as Prime Minister by Sir Alec Douglas-Home, who was defeated in the 1964 general election.