Why was Churchill voted out in 1945?

[Lomax]

The slogan at the time was "Cheer Churchill, Vote Labour."

He was an extremely popular war-time leader; but the nation was tired of war. They were also tired of a lot of other things. There was a prevailing national mood that the post-war era (by the way, Churchill was voted out before WW2 actually ended) would be a time to build something new, and better than what had gone before. Better housing, better education, better health provision...

This process had actually started during the war. Whilst Churchill ran the war, to a great extent Attlee ran the country, and did a lot of the groundwork while he was deputy PM. See the Beveridge report, for example.

A significant consideration is that the Khaki Vote - votes cast by troops serving overseas - was Labour almost to a man.