According to several sources (though, possibly, all traceable back to Hugh Dalton), Herbert Morrison opposed leaving the coalition as early as Labour did. If he was leader instead of Attlee, there is potential for the Labour Party to stay in the coalition at least long enough for Churchill to gain the upper hand. Morrison might even be willing to go for a coupon election, keeping the coalition together into the next Parliament. The Tories will have time to rebuild their party machine and get PR going on their image. Meanwhile, Labour will begin to split as the left agitates for it to leave the coalition - and many supporters might well start to view it as a puppet of the Tories and transfer their loyalty to the Common Wealth Party or the Communists. The Tories get to do to Labour the same thing they did to the Liberals after WWI.
Churchill's post-war government is going to be an absolute disaster, one from which Britain might never recover. There will be famines in the north, homelessness dragging on well into the 1950s, bloody war in the colonies until Britain is stripped of them by the UN, insurrection in the army, mass strikes, the collapse of the coal industry and rail network. The foundations of the prosperity that Britain enjoyed in the 50s, 60s and early 70s will never be laid. As things get worse, there may be a backlash from the government, the hardline repression of political opposition - and there will be the constant threat of an unpopular war with the Soviets. Imagine a boot stamping on a human face until Churchill is forced into retirement. We'll probably end up like Italy and Greece (complete with America intervening to stop the rise of the communists in the early 1950s), though there is some hope that a reunified Labour Party could gain power in the 1950s and do some Scandinavian things.