King Edward VIII was King of the UK for a little under a year in 1936. He was an open admirer of Hitler's. He abdicated for unrelated reasons. However, when the war began, he was seen as a liability and likely to undermine the war effort, so he was assigned to be the governor of the Bahamas to get him out of Europe.

In terms of terrorism, the IRA launched a bombing campaign in Britain in the summer of 1939. They also solicited Nazi aid during the war. The majority of the organisation were probably not ideological sympathisers.

Prior to the war there was considerable support for Hitler, especially in Oswald Moseley's British Union of Fascists. This was banned in 1940 and several hundred members were interned.