Gary Oldman doubted he could play Winston Churchill in 'Darkest Hour' - because he was worried about having to gain a lot of weight.

The 59-year-old film legend stars as the heroic British Prime Minister, the man who guided Great Britain and its allies to victory against the German Nazis in World War II, in JOE WRIGHT's new film.

Churchill's figure was much more portly than Oldman's and he was concerned that if he had to ''gain 70 pounds'' for the part he'd never lose it, but luckily he was able to achieve the required look with makeup and the right prosthetic.

Speaking at the UK premiere of 'The Darkest Hour' at the Odeon Cinema in London's Leicester Square on Monday evening (11.12.17), Oldman said: ''I laughed and thought don't be ridiculous. I'm coming up to a milestone, I'm nearly 60. And I thought there was no way on earth that I could gain 70 pounds and then spend the rest of my life of what remains losing weight. That would be the option. And so makeup was really the only way to go with it. You have this icon and this man who has been so mythologised. The silhouette is so iconic and so famous and I really wondered if one could get past all of that and find the man.''

'Darkest Hour' tells the story at the beginning of World War II as within days of becoming Prime Minister, Churchill must face one of his most turbulent and defining trials: exploring a negotiated peace treaty with Nazi Germany which could guarantee Britain's independence and that of the Commonwealth.

As the Nazi forces roll across Western Europe and the threat of invasion of the UK, Churchill must resist attempts to by his own political party and an initially sceptical King George VI, to stand firm against the dangers facing his country and not buckle to the Nazis.

Oldman - who has been nominated for the Best Actor Golden Globe for his performance - stars alongside Kristin Scott Thomas, Lily James and Ben Mendelsohn in 'Darkest Hour'.