She is the British actress whose surprise nomination for the Best Actress Oscar stunned Hollywood this week and seemed to herald her elevation to the A-list.

But just days later Andrea Riseborough is at the centre of an extraordinary probe into whether any rules were broken in selecting the shortlist for the Academy Awards.

The film world had been astonished when her portrayal of an alcoholic in independent film To Leslie had received the nomination. The little-seen movie had taken just £22,000.

Stars including Gwyneth Paltrow, Kate Winslet, Mia Farrow, Susan Sarandon, Minnie Driver and Edward Norton had praised Riseborough’s performance in the low-budget drama, released in October. And Paltrow, Jennifer Aniston, Charlize Theron and Courteney Cox hosted private screenings of the movie and voiced support for Riseborough.

The film world had been astonished when Andrea Riseborough’s portrayal of an alcoholic in independent film To Leslie had received the nomination

Many share the same powerful Hollywood agency as Riseborough, who has long been admired for her performances in films such as Birdman and Battle Of The Sexes but is largely unknown in America.

For To Leslie, Riseborough had not been nominated for a Golden Globe or Critics Choice award, the traditional ‘route’ to the Oscars.

Her nomination drew ire from some who believe acclaimed black actresses Viola Davis (The Woman King) and Danielle Deadwyler (Till) would have made the Best Actress list until the A-list campaign for Riseborough kicked off.

On Friday the Academy of Motion Picture Arts and Sciences said it would immediately launch a review to see if any of its rules – including one which bans ‘direct solicitation’ of votes from members – were broken. If they were then Ms Riseborough could be stripped of her nomination.

A producer who is an Academy voter said: ‘Andrea is one of the best actors working today and beloved by her peers but her Oscar nomination shocked everyone. It wasn’t just a shock, it was a miracle. You could hear the gasps when her name was read out in the room. This is a film no one had seen or heard of until recently.

‘Both Viola and Danielle turned in stunning performances and one or both were expected to be nominated. There has been a lot of backlash this week that, yet again, a white woman may have pushed out equally-worthy black actresses, who never received anything like the support Andrea got.’

The nomination drew ire from some who believe acclaimed black actresses Viola Davis (The Woman King) would have made the Best Actress list

Others argued Danielle Deadwyler (pictured) would have made the Best Actress list until the A-list campaign for Riseborough kicked off

The campaign for To Leslie drew further attention when several stars, including Mia Farrow, used the same phrasing in social media posts, calling it ‘a small film with a giant heart’. Online entertainment site Puck reported the probe would centre around an email sent to A-list stars and Academy voters, allegedly from a source close to the film, which said: ‘If you’re willing to post every day between now and Jan 17th, that would be amazing!’

The source said: ‘Does that violate Academy rules? It’s close.

‘You are not allowed to directly solicit voting members.’

Earlier in the week, Riseborough said of her nomination: ‘I’m astounded.’ Her spokesman has refused to comment.

The other nominees for Best Actress are Cate Blanchett (Tar), Michelle Yeoh (Everything Everywhere All At Once), Michelle Williams (The Fabelmans) and Ana de Armas (Blonde).