Gary Oldman suffered ''serious nicotine poisoning'' after smoking 400 cigars while filming 'Darkest Hour'.

The 59-year-old actor portrays iconic former Prime Minister Winston Churchill - who was renowned for his smoking habit - in the upcoming biopic, and threw himself so into character, he got through almost $20,000 worth of tobacco during the 48-day shoot.

He admitted in an interview with The Hollywood Reporter: ''I got serious nicotine poisoning.

''You'd have a cigar that was three-quarters smoked and you'd light it up, and then over the course of a couple of takes, it would go down, and then the prop man would replenish me with a new cigar -- we were doing that for 10 or 12 takes a scene.''

But director JOE WRIGHT felt it was necessary for the movie.

He said: ''It's Winston Churchill. You can't have Winston Churchill without a cigar.''

Meanwhile, Gary recently admitted he was worried about gaining weight for the role as he didn't think he would lose it again.

He 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.