The National Socialist League was a short lived political movement in the United Kingdom immediately before the Second World War.

The NSL was formed in 1937 by William Joyce, John Beckett and John Angus MacNab as a splinter group from the British Union of Fascists. The leaders claimed that the League had been formed because BUF leader Oswald Mosley refused to make Adolf Hitler the main inspiration instead of Benito Mussolini, although Mosley contended that the three had simply been sacked from their paid posts in the BUF as part of a cost-cutting exercise.

Whatever the truth the NSL began fairly healthily as Joyce secured the financial backing of Alex Scrimgeour , a stockbroker, and soon the NSL was able to publish its own mewspaper, The Helmsman, adopting 'Steer Straight' as the party motto. Rising far right figure A. K. Chesterton would go on to speak at a number of NSL functions, although he never formally joined the movement. However the party failed to attract members as war with Hitler began to look increasingly inevitable and initial optimism faded.

The NSL began to unravel in 1938. Beckett became disillusioned with Nazism after the Munich Crisis and left the NSL, re-emerging later in the British Peoples Party. Scrimgeour died soon after this and surprisingly left nothing to the NSL in his will, cutting off essential funding. Membership fell to around 40 people by 1939 and before Joyce emigrated to Germany he entrusted MacNab with the job of winding the League up. It had come to an end just before war broke out and did not re-emerge.