Worse election defeat

[Gary J]

There have been worse defeats, in UK politics. The non-coalition Liberals in 1918, went from the clear Official Opposition to no more than 36 MPs. The undivided Liberal Party was the leading party in the wartime coalition until 1916. After 1918 the official party never recovered first or second place in the House of Commons.

[Gary J]

I didnt select parties which were wiped out to an extent that they never won again.

OK, how about the British Labour Party in 1931. 287 seats out of 615 in the 1929 general election, when they were the largest party and formed a minority government. A small split over austerity measures during the Great Depression, led PM Ramsay MacDonald to form a National government. The Labour Party was crushed in the 1931 general election, electing 52 seats out of 615 including 6 unendorsed candidates. The party was back in government during the 1940-45 wartime coalition, before winning a large majority in the 1945 general election.