The British Union of Fascists (BUF) was a political party of the 1930s in the United Kingdom. The party was formed in 1932 by ex-Labour government minister Sir Oswald Mosley and was a union comprised of several small, extreme nationalist parties.

Mosley modelled himself on another fascist leader, Benito Mussolini. He also modeled his party along the lines of fascist movements in other countries, primarily Italy.

He instituted a black uniform, gaining the party the nickname blackshirts. The BUF was anti-communist and protectionist. It supported the replacement of parliamentary democracy with a system of elected executives with jurisdiction over their own industries - something similar to the corporatism of the Italian fascists. The BUF claimed a membership as high as 50,000 at one point, and the Daily Mail was an early supporter, famously running the headline "Hurrah for the Blackshirts!"

Opinion was divided in response to the BUF's black shirted followers; in some quarters, their unified appearance, and the vision of militant Britishness they presented, won the party supporters. Others found in them something absurd. P.G. Wodehouse, for example, based the 'amateur dictator' Roderick Spode, who appears in his Jeeves and Wooster stories, on Mosley.

Despite considerable resistance - sometimes violent - from Jewish people, the Labour Party, assorted democrats and the Communist Party of Great Britain, they still found a following in the East End of London, where in the London County Council elections of 1937 they obtained good results in their strongholds of Bethnal Green, Shoreditch and Limehouse. However the BUF never faced a General Election - feeling unready in 1935, they urged voters to abstain, offering the promise of "Fascism Next Time".

Towards the middle of the 1930s, the BUFs increasingly violent activities, and a growing discomfort at their alignment with the German Nazi party, began to alienate some of their middle-class supporters. Membership accordingly decreased. At a rally in London, in 1934, BUF stewards became involved in a violent confrontation with militant communists, and this bad publicity caused the Daily Mail to withdraw its support from the party.

Many of the party's members were drawn from aristocratic and military families and included celebrated military man J.F.C. Fuller.

With its lack of electoral success, the party was drawn away from mainstream politics and further toward extreme anti-Semitism during 1934-1935. They organised several anti-Semitic marches and protests in London, such as the one that resulted in the famous Battle of Cable Street in October 1936). Nonetheless, membership fell to below 8,000 by the end of 1935. The government was sufficiently concerned, however, to pass the Public Order Act of 1936, which banned the wearing of political uniforms during marches, required police consent for political marches to go ahead, and effectively destroyed the movement. The BUF was completely banned in May 1940, and Mosley and 740 other senior fascists were interned for much of World War II.

Mosley made several unsuccessful attempts at a political comeback after the war, most notably in the Union Movement.