Anthony McCarten thinks Gary Oldman took his portrayal of Winston Churchill to a ''whole new level'' and his work on 'Darkest Hour' is the ''performance of his lifetime''.

The 56-year-old screenwriter wrote the new Joe Wright movie - which follows the hero British Prime Minister at the beginning of World War II - and McCarten thinks Oldman is more than a worthy Best Actor nominee at the Golden Globes.

Speaking exclusively to BANG Showbiz at the UK premiere of the new movie at the Odeon Cinema in London's Leicester Square on Monday night (11.12.17), McCarten said: ''When you write a role like Winston you want to write a role that an actor, when they do it, will be magnificent. You have to write magnificent into the script but then someone has got to do it. And Gary then took what I did and took it to a whole new level and I think it's the performance of his lifetime or of most actors' lifetimes.''

'Darkest Hour' tells the true story at the beginning of World War II and within days of becoming the UK's leader, Churchill must face one of his most turbulent and defining trials: exploring a negotiated peace treaty with Nazi Germany and deciding whether to back out of conflict in return for assurances Adolf Hitler's army will leave Britain alone.

McCarten spent eight hours writing the script for the film and he admits he did a lot of research into the famous political figure to show sides of Churchill that hadn't be portrayed before.

He said: ''I did a bit more research and then found out, not only was there pressure, he yielded to it to some degree and seriously consider a peace deal but then he changed his mind and that was key. And I thought I want to write a movie about a guy who can change his mind. I thought that ability to change his mind was not something that we generally were lead to believe about Winston.

''We've never seen the humorous Winston yet he is really beloved for his sense of humour but we've never seen him as a witty man, the witty Winston. And we have never seen a romantic Winston, the letters he wrote to (his wife) Clementine reveal a very romantic emotional side. So it was just all these colours to play with that no one has ever played with before and then you give it all to an actor like Gary Oldman and see what happens.''