When she was offered the role of wartime prime minister Winston Churchill’s wife Clementine in the new movie Darkest Hour she knew that the film had all the ingredients for critical and commercial success. 

But despite having top director Joe Wright at the helm, Gary Oldman playing Churchill and a lavish budget to match, she flatly refused to accept the part. 

“They weren’t giving Clemmy – me – enough to do,” she explains.

“I told him he could get any old person to do this. 

“So he rewrote the part to make it what it is now. 

“I still think there’s more to be told about her. 

“She was an amazing woman.”  

The result is an engrossing film on what was indeed Britain’s darkest hour in 1940 as we stood alone against Nazi Germany. 

While Oldman, heavy with prosthetics, was an unlikely choice to play Churchill his brilliant performance has made him hot favourite to win the best actor prize at this weekend’s Golden Globe Awards. 

Scott Thomas delivers an equally impressive performance as a wife who gives as good as she gets. 

In the film Churchill has to keep Britain’s morale high and courage steady as our only remaining ally – France – surrenders in June, 1940. 

Hitler closed in to make detailed invasion plans to defeat the only country which remained defiant. 

Scott Thomas, 57, who makes the most of her own defiance in giving Clementine a proper role in the partnership, has always had the ability to surprise. 

She closely identified with what Churchill called his “black dog” of depression.  

“I know from personal experience how debilitating depression can be,” she says. 

“I suffered in my late teens and could hardly get out of bed at times. 

“You walk around not taking anything in.”

She also appreciates a life of sacrifice and service, with which the Churchills were steeped. 

Scott Thomas’s father Simon, a pilot in the Royal Navy Fleet Air Arm, was killed in a flying accident when she was four.

Her stepfather, another Royal Navy pilot also called Simon, was killed in a freak accident when she was 11. 

She was sent away to the prestigious Cheltenham Ladies College by her mother Deborah and hated her time there.  

“Boarding school is a wicked thing,” she says flatly. 

“Life and circumstance has made me build up reserve. 

“But if I read another description of me being icy or needing to thaw out I will throw up. 

“It is a matter of self-protection. 

“I do not want to pour my heart out to the world. 

“I am cautious in what I say.” 

Clementine Churchill, who was nicknamed “Cat” by her husband, had a similar attitude. 

“I have played her exactly as she was in life, a fighter with a husband who was full of doubts and insecurities. 

“He once said that marrying her was his life’s greatest achievement. 

“It was important in the film to show why that was so.

“She was strange looking with clothes and hair from another age, formidable in every way.” 

Scott Thomas completed her research by talking to one of her surviving secretaries, plus grandchildren. 

“A lot of people were terrified of her,” she reveals. 

“But others loved her absolutely.”  

Scott Thomas knows about the highs and lows of opinion. 

“When I started out as an actress people were as obsessed about weight and fat-ism as they are today. 

“I was more than 12 stone by my early 20s. 

“When I shopped for clothes it was a case of, ‘Put that on in a size 16, love’. 

“But people like Kate Winslet have spoken out about the Hollywood obsession with weight. 

“She’s fantastic because the whole thing does not wash with her. 

“People make comments about some women along the lines of, ‘She’s beautiful but she’s fat’.  

“That should never be an issue. 

“I didn’t go on a diet.

“The weight fell off me when I got married [to French gynaecologist Francois Olivennes at the age of 27] but there were many setbacks before that. 

“I was told by someone at the Central School of Speech and Drama in London that I would never make an actress. 

“So I went to work in Paris at 19 as an au pair and studied at drama college in France. 

“It was a struggle all the way.” 

And when she finally made her film debut at 25 in 1986’s Under The Cherry Moon, with the late pop star Prince who also directed, it was laughed off the screen.  

It received five Golden Raspberry awards, including worst picture, as the biggest flop of the year. 

Her eventual role as Fiona in the 1994 surprise hit film Four Weddings And A Funeral proved to be a key stepping stone. 

Her character had been madly in love with Hugh Grant’s Charles for years and told him so in a touching scene of unrequited love. 

She also outshone the wooden acting of star Andie MacDowell by a Hollywood mile and was handed a Bafta award as best supporting actress. 

It kick-started a film career on a grand scale. 

She won a best actress Oscar nomination playing the unfaithful wife in The English Patient (1996) before playing the female lead opposite two of the world’s biggest stars: Robert Redford in The Horse Whisperer (1998) and Harrison Ford in Random Hearts in 1999.  

But the Hollywood big time was not for her. 

“I was working with some extraordinary men in back-to-back films but it was such a palaver. 

“Then suddenly I had a call asking me to work in French theatre. 

“My gut instinct was ‘yes’ so I agreed. 

“So many people in Los Angeles asked, ‘Why on earth would you do this? 

“You are just getting established as a Hollywood actress. 

“Why give it up?’  

“But I simply did not want to be miles from home and far from Europe. 

“There were big decisions to be made on my personal life and family. 

“I suddenly realised I did not want to become a Hollywood film star and the thought of working in theatre in the depths of France became very attractive.” 

The result is that she shared a busy family life with children Hannah, 29, Joseph, 26 and George, 17. 

She is now divorced from her husband but is clearly enjoying being a grandmother to Hannah’s baby daughter. 

“I understand the order of things, everything has fallen into place,” she says. 

“It’s an extra ordinary experience looking down on this tiny little baby which is looking up at you and there are two things on its face, love and trust.”  

She has also been able to move between small-budget European movies, Hollywood roles and leading stage performances. 

“Once I reached 50 I realised it was a dangerous age for an actress. 

“So why not live it dangerously?” 

And that is exactly what Scott Thomas, who was awarded a damehood in 2015, has been doing with varied roles in recent years. 

Some have been in French movies such as The Woman In The Fifth or classic British films such as Invisible Woman, neither of which made any box office impact. 

“At one point I just got fed up with filming,” she says. 

She was in Sally Potter’s black comedy The Party, released just a few weeks ago, which received rave reviews.  

Darkest Hour looks set to receive similar plaudits. 

“There is that Eldorado of being a Hollywood star and I still wake up with a pang of envy for those who are,” she admits. 

“You know, glorious film star being adored! 

“But I am allowed to go off and make films for directors like Sam Taylor-Wood [Nowhere Boy, in 2010, in which she played John Lennon’s strict Aunt Mimi]. 

“If I was locked into a Hollywood persona of being a film star I would not be able to do that.” 

Darkest Hour is released on Friday, January 12.