On the subject of Churchill,
Germanys militarisation and march to war could be seen as an attempt at not being out-competed and sidelined by the power of the British Empire- which Churchill was no small part of, and nor was he afraid, as others have pointed out to use morally dubious tactics to maintain its power.
so despite helping to abolish Road Tax- he's out!
I'm gonna be predictable and say Charles Darwin, who was modest, concienscious, and caring and gave something positive back to the whole world, not just Britain.
(anyway, if we have to pick war-mongers from the British isles, I'd say CuChulainn!)