The Revolutionary Socialist Party, initially known as the International Socialist Labour Party, was a political party in Britain. It emerged from a Scotland-based faction of the Socialist Labour Party, which had left the SLP in the early 1930s. The party was mainly based in Edinburgh, where it had its office and most of the party members lived. Members were also present in Glasgow, Aberdeen and Yorkshire. The party published The British Revolutionary Socialist.
RSP took part in conferences of the London Bureau as an observer. The party approached the Independent Labour Party about a merger in 1937, which the ILP rejected on the grounds that the RSP was under trotskyist influence. The party then began orienting itself towards the Fourth International.
The RSP was invited to and took part in the 'National Conference of Bolshevik-Leninists', held on 30 July – 31 July 1938. Through this conference, the RSP merged into the Revolutionary Socialist League.