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 after being misdiagnosed with cancer. He was replaced as Prime Minister by Sir Alec Douglas-Home, who was defeated in the 1964 general election.

Maurice Harold Macmillan, 1st Earl of Stockton, (10 February 1894 – 29 December 1986) was a British Conservative politician who was Prime Minister of the United Kingdom from 1957 to 1963. Caricatured as "Supermac", he was known for his pragmatism, wit and unflappability.

Macmillan was badly injured as an infantry officer during the First World War. He suffered pain and partial immobility for the rest of his life. After the war he joined his family book-publishing business, then entered Parliament at the 1924 general election. Losing his seat in 1929, he regained it in 1931, soon after which he spoke out against the high rate of unemployment in Stockton-on-Tees. He opposed the appeasement of Germany practised by the Conservative government. He rose to high office during the Second World War as a protégé of Prime Minister Winston Churchill. In the 1950s Macmillan served as Foreign Secretary and Chancellor of the Exchequer under Anthony Eden.

When Eden resigned in 1957 following the Suez Crisis, Macmillan succeeded him as prime minister and Leader of the Conservative Party. He was a One Nation Tory of the Disraelian tradition and supported the post-war consensus. He supported the welfare state and the necessity of a mixed economy with some nationalised industries and strong trade unions. He championed a Keynesian strategy of deficit spending to maintain demand and pursuit of corporatist policies to develop the domestic market as the engine of growth. Benefiting from favourable international conditions, he presided over an age of affluence, marked by low unemployment and high—if uneven—growth. In his speech of July 1957 he told the nation it had 'never had it so good', but warned of the dangers of inflation, summing up the fragile prosperity of the 1950s. He led the Conservatives to success in 1959 with an increased majority.

In international affairs, Macmillan worked to rebuild the Special Relationship with the United States from the wreckage of the 1956 Suez Crisis (of which he had been one of the architects), and facilitated the decolonisation of Africa. Reconfiguring the nation's defences to meet the realities of the nuclear age, he ended National Service, strengthened the nuclear forces by acquiring Polaris, and pioneered the Nuclear Test Ban with the United States and the Soviet Union. After the Skybolt Crisis undermined the Anglo-American strategic relationship, he sought a more active role for Britain in Europe, but his unwillingness to disclose United States nuclear secrets to France contributed to a French veto of the United Kingdom's entry into the European Economic Community. Near the end of his premiership, his government was rocked by the Vassall and Profumo scandals, which to cultural conservatives and supporters of opposing parties alike seemed to symbolise moral decay of the British establishment. Following his resignation, Macmillan lived out a long retirement as an elder statesman. He was as trenchant a critic of his successors in his old age as he had been of his predecessors in his youth. In 1986, he died at the age of 92.

Macmillan was the last British prime minister born during the Victorian era, the last to have served in the First World War and the last to receive a hereditary peerage.