Gary Oldman got nicotine poisoning on the set of his upcoming movie 'Darkest Hour' because he had to have a cigar all the time to portray British World War II Prime Minister Sir Winston Churchill.

The 59-year-old actor portrays the leader in the new biopic by JOE WRIGHT and to accurately play Churchill as he battled Adolf Hitler and the Nazis he had to don a fat suit and take up the smoking habit which the heroic history maker.

But Oldman's body struggled to cope with the high levels of nicotine from the cigars and he got ill.

Speaking to Variety Studio Presented by AT&T, Oldman said: ''It is what it is. It took four hours a day to get into the fat suit and 45 minutes to take it off. You just focus. I think I hold the record now. I think it was 50 consecutive days in it. It's like a mindset you have. Like running a marathon. Once in it, it was very comfortable apart from a bout of nicotine poisoning. It's not pretty. Especially when you're in a fat suit.''

The plot focuses on a crucial moment at the beginning of WWII when Churchill has to make a key decision as to what to do to stem the Nazi march across Europe.

Wright admits making the movie was an ''exercise in education'' and ahead of the cameras rolling on 'Darkest Hour' he spent a long time reading and talking about Churchill.

He said: ''Every film that I take one is an exercise in education. I've had amazing teachers throughout my life and career. We spent a long time thinking and reading and talking about Winston. We wanted to bring this icon down from his pedestal and bring him eye to eye and discover the real man and all his humour, wisdom and faults.''

Oldman also stars alongside Kristin Scott Thomas, Ben Mendelsohn and Lily James in the movie which is slated for release at the end of the year.