"There was a lot of support for Hitler in Britain." I would like to hear your definition of "a lot", Ronald. In the history books I read, Britain was the one European nation, which held out against Hitler in 1940, when the rest of Europe had either been defeated or cowed into reticence. As thousands of defenceless Britons sailed pleasure craft in and out of Dunkirk to rescue the BEF, under bomb and bullet attack, I don't think we can look there for "a lot of support for Hitler".
Joseph Kennedy advised his government that Britain was finished and the Irish Republic declined to pick a quarrel with Herr Hitler.
Sir Oswald Mosley was indeed a Fascist and a brute. It is less clear whether he was a traitor. He often protested loudly that he would have fought the Germans himself had they landed in the UK.
Using the preposterous William Joyce as a stick with which to beat the British really has to be laughed off. His nationality was something of a grey area, as you will discover if you bother to read the link I have provided.
Yes, Britain had a few traitors in the Second World War. The other side of the coin is that Britons lost thousands of homes, limbs and lives to resist evil when some other countries did nothing. That is what I call "a lot".