What if Churchill still stayed in the Liberal Party. Assume that instead of shifting to the right, he continued his prewar trajectory of shifting to the left (in 1918 he was even a supporter of railway nationalization), thus becoming a centre-left politician like Lloyd George. Haldane proved that you can be centre-left but still Imperialist.
How would this affect British politics, especially the 3-4 years preceding the Second World War? Who would become the war leader? We already know that Churchill was the biggest opponent of appeasement, and in this scenario he would be in Lloyd George wing and likely succeed him as Liberal Leader rather than Samuel, while Sinclair was his closest comrade.