Wolverhampton East was one of the last urban constituencies which the Liberals managed to hold against both Labour Party and Conservative Party opposition up to 1945. Mander was expected to be nominated Chief Whip for the Liberal Party in the House of Commons, but he lost his seat at the 1945 general election, in the post-war Labour landslide. Considering that Labour had now replaced the Liberals as the main representative of the radical tradition in British politics, he joined the Labour party in 1948, and subsequently served as a Labour member of the Staffordshire County Council.