The Battle of Cable Street was a series of clashes that took place at several locations in the inner East End, most notably Cable Street, on Sunday 4 October 1936. It was a clash between the Metropolitan Police, sent to protect a march by members of the British Union of Fascists led by Oswald Mosley, and various de jure and de facto anti-fascist demonstrators, including local trade unionists, communists, anarchists, British Jews and socialist groups. The anti-fascist counter-demonstration included both organised and unaffiliated participants.

The British Union of Fascists (BUF) was a British fascist political party formed in 1932 by Oswald Mosley. Mosley changed its name to the British Union of Fascists and National Socialists in 1936 and, in 1937, to the British Union. In 1939, following the start of the Second World War, the party was proscribed by the British government and in 1940 it was disbanded.

The BUF emerged in 1932 from the electoral defeat of its antecedent, the New Party, in the 1931 general election. The BUF's foundation was initially met with popular support, and it attracted a sizeable following, with the party claiming 50,000 members at one point. The press baron Lord Rothermere was a notable early supporter. As the party became increasingly radical, however, support declined. The Olympia Rally of 1934, in which a number of anti-fascist protestors were attacked by the paramilitary wing of the BUF, the Fascist Defence Force, isolated the party from much of its following. The party's embrace of Nazi-style anti-semitism in 1936 led to increasingly violent anti-fascist confrontations, notably the 1936 Battle of Cable Street in London's East End. The Public Order Act 1936, which banned political uniforms and responded to increasing political violence, had a particularly strong effect on the BUF whose supporters were known as "Blackshirts" after the uniforms they wore.

Growing British hostility towards Nazi Germany, with which the British press persistently associated the BUF, further contributed to the decline of the movement's membership. It was finally banned by the British government in 1940 after the start of the Second World War, amid suspicion that its remaining supporters might form a pro-Nazi "fifth column". A number of prominent BUF members were arrested and interned under Defence Regulation 18B.