He won an Oscar for Tinker Tailor, Soldier Spy but it was just delayed until The Darkest Hour ie everyone thought he should have gotten the Oscar (anyone remember who won without looking on Google?) so quickly voted for him on his next good performance. Oldman was good as Churchill but he acted beautifullly in Tinker Tailor, Soldier Spy.
I'm pretty sure there was humour in my comment but it doesn't translate well for some people.