Churchill definitely exceeds his contribution, and downplays his mistakes. For me one of his falsehoods is his claim to have been battling against members of the Government who were in favour of surrender. Then again most historians and writers tend to judge him pre becoming PM as a hero / legend in waiting.
I am always amused by the number of people who reference listening to a Churchill speech inspiring them. The speeches referenced were delivered in Parliament only, and were recorded after the war.