The actor touches on the haunted frailty of Britain’s wartime leader in a new film focusing on the run-up to D-Day.

He has played Hermann Goering and Joseph Stalin. Now, after those monsters of the 20th century, comes a portrayal of one of its heroes. Brian Cox is taking on the role of Winston Churchill in a new film, for which he put on 10 kilos, shaved his head and practised Churchill’s distinctive jutting lower lip.

But beyond making “certain physical concessions”, Cox says he was determined not to do the obvious thing and caricature the cigar-smoking statesman by adopting the stereotypical “Churchillian voice”. Cox, a Royal Shakespeare Company associate artist, is the latest in a long line of actors who have played Britain’s most celebrated leader, including Richard Burton, Robert Hardy and Albert Finney.

 He likened Churchill to great Shakespearean characters such as King Lear, a role he played to acclaim at the National Theatre. “The problem with Churchill is that you always fall into this trap of ‘the Churchillian voice’,” he said.

After listening to rare private recordings, Cox realised that Churchill’s natural voice was quite different from that of the rousing speeches with which he rallied the British people during the second world war.

He said: “I kind of discovered that the Churchillian voice was very much part of his oratory style – something he created. So there’s a bit where I do ‘my Churchill’ … but for most of the film, I really don’t talk like that because he was very quick and much more mercurial in his language.”

As an orator, Churchill would, for example, place a drawn-out emphasis on the “a” in a word like “France”. It was Cox said, “a clever technique”.

The film, Churchill, shot in Scotland, focuses on the run-up to D-day in summer 1944, portraying the prime minister as a man fearful of history repeating itself. Operation Overlord, the cross-Channel assault, brought back memories of his disastrous Dardanelles campaign in 1915, when thousands of young men were killed and wounded. Cox said: “The vision of the beaches is the vision of the destruction in Gallipoli.”

The film will also bring out the role played by his wife Clementine in saving him from physical and mental collapse and inspiring him to greatness. “Clemmie” is played by Miranda Richardson, whose previous films include Tom & Viv, about the poet TS Eliot.

Cox said Churchill, exhausted by the war and illness, was plagued by depression: “Clemmie was his rock. She keeps him on the straight and narrow, but is also quite exhausted by him and by his mood swings. I think he’s full of flaws and someone who lives with his mistakes, and that was a great source of his depression.”

He added: “There was an element of loneliness. He was alone for so much of the time because he was always against the flow. When Neville Chamberlain came back from Munich with his little piece of paper – peace in our time – Churchill didn’t buy it for a minute. People didn’t like him because he stated what he believed. That’s what made it very hard for him. Eventually that amount of rejection has to get to you. But he was proved right on so many elements of the second world war.”

As an actor, portraying both strength and frailty is hard, Cox said. “It’s frailty of spirit as much as physical frailty.” Playing Churchill was humbling and inspiring: “How lucky I am to give persona to this amazing man.”

He is now having difficulty losing the weight, but prosthetics and padding would not have worked: “You have to have the weight. He was not a tall man, but he was big. You can’t be walking around in padding. His walk is very easy: there’s a sort of shuffle about him.”

Other recent portrayals include those of Michael Gambon in Churchill’s Secret and John Lithgow in The Crown, both for TV. Later this year, Gary Oldman will be seen in the role in Darkest Hour, by Joe Wright, director of Pride and Prejudice.

Does Britain need a Churchill more than ever today? Definitely, Cox believes. Referring to Boris Johnson, the foreign secretary and author of a Churchill biography, he said: “[Churchill] wasn’t like the bunch of chancers we’ve got now, who are not a patch on him. Boris Johnson can bleat all he likes, but he ain’t no Winston Churchill.”

Churchill always put the country before himself, he added: “He had a vision, a great heart and a great sense of caring.”

Churchill will be released in June to coincide with the 73rd anniversary of D-Day

PAST LIVES

Richard Burton

The Gathering Storm (1974)

Writing in The New York Times before the drama was aired in the US, Burton said that while preparing to play Churchill, “I realised afresh that I hate Churchill and all his kind.” The BBC banned him from future productions.

Robert Hardy

The Wilderness Years (1981)

Robert Hardy, who has played Churchill nine times, first took on the role for this ITV mini-series. He later described the role as the greatest challenge of his acting career. He spent nine months “listening – morning, afternoon and evening – to 24 double-sided LPs of all the speeches he’d made.”

Albert Finney

The Gathering Storm (2002)

Finney, who stars with Vanessa Redgrave as Clementine, won both a Bafta for best actor and an Emmy for outstanding lead actor. The BBC-HBO film also featured a young Tom Hiddleston as Randolph Churchill.