Since 1940 Labour Action for Peace has worked alongside the Labour Party promoting it as the Party for and of Peace

http://labour-peace-action.org.uk/about-us/

Founded in 1940 by six peace activists including George Lansbury MP, Labour Action for Peace (LAP) has been active in promoting peace, opposing war and working inside the Labour Party and wider labour movement to keep peace and disarmament issues to the forefront of Labour’s policies.

http://new.labour-peace-action.org.uk/wp-content/uploads/2017/11/LAP-Membership.pdf