Answer
Banned after WWII, the British Union of Fascists (BUF) met its demise due to its strong association with Nazi Germany and Adolf Hitler. The BUF's leader, Sir Oswald Mosley, was detained during the war and the party's activities were heavily restricted. Despite attempts to revive the party in the postwar years, the BUF never regained its pre-war prominence and eventually faded into obscurity.