Apart from the impossibility of Britain waging war with Germany and Russia also bear in mind that members of Britains Labour party greatly admired the Russians for their revolution, of course they had no idea what Stalins Russia was actually like.
There were a small number of communists in Britain and a small fraction of these belonged to the Labour Party, the Labour Party however represented the acceptable face of capitalism rather than its unacceptable face. The majority of those in Britain that supported the lunatic fringes of politics had their roots in the Tory Party, both the Daily Telegraph and Daily Mail were huge advocates of Adolf Hitler and the Nazi Party, there were in fact a great number of pro Nazi defeatists within the Tory party and good old Winston had first to tread them into the ground in order to save Britain from surrender.