Alan Thornett is a British Trotskyist leader. Then a car worker in Oxford, Alan Thornett was recruited to Gerry Healy's Socialist Labour League in the early 1960s. He helped to build a formidable support for Trotskyist ideas in the Cowley Oxford plant during the 1960s and early 1970s.

However, in 1973 he and most of the Cowley group were expelled from the SLL along with up to 500 other members of the SLL. Some of them went on to form the Workers Socialist League (WSL) of which Thornett was the senior leader. An international tendency of groups expelled from Healy's ICFI existed for a period known as the Trotskyist International Liaison Committee.

However the WSL foundered after losing members to the Spartacist League and gradually losing its basis of support as industrial struggle tailed off in the late 1970s. The WSL fused with Sean Matgamna's group the I-CL in 1981, only to leave again in 1983 somewhat smaller.

Now in the Labour Party Thornett's group went by the name the Socialist Group until it fused with the International Group to form the International Socialist Group (ISG). Thornett is now leader of the ISG which is affiliated to the United Secretariat of the Fourth International. The ISG has since left the Labour Party and is involved in the Socialist Alliance, supporting most recently the absorption of the SA into George Galloway's Respect - the Unity Coalition . Thornett sits on the Respect National Council. He is the author of two volumes of autobiography.