Katie Jarvis, 17, has signed to the United Talent Agency — which represents stars including Johnny Depp, Harrison Ford and Gwyneth Paltrow.

Ms Jarvis won her part in Andrea Arnold's film Fish Tank when she was spotted by a scout arguing with her boyfriend at the railway station in her home town of Tilbury, Essex.

She could not attend the film's opening in Cannes because she had her daughter, Lily Mae, the Saturday before.

But as soon as the Americans saw her on-screen, talent agent Billy Lazarus flew to the UK to meet and sign her at the weekend.

A UTA spokesman said: “Katie is an undeniable natural talent and we're excited to get into business with her at this early stage of her career.”

An insider said agents in America had heard of her before the film opened on the second day of the Cannes Film Festival last week.

When they finally saw her performance — as a feisty tearaway thrown into emotional turmoil by her mother's new boyfriend — they knew she was special.

Critics praised her performance as “astonishing” and “tremendous”. There is even a buzz she might win best actress in Sunday's end-of-festival awards.

In Britain, Ms Jarvis had been signed by Sue Latimer of ARG, who represents stars including Daniel Radcliffe. The two agencies will co-represent her.

Ms Jarvis's success is even more striking than that of Sam Riley, who had been working in a warehouse in Leeds when he was cast as Ian Curtis in the biopic Control and lauded at festivals two years ago. At least he had enjoyed an earlier career as a rock star.

A spokeswoman for Ms Jarvis said she was busy with her new baby and not giving interviews just yet. But she added: “I think Katie's brilliant. She's 18 in a few months time, has had a baby and is the toast of Cannes. It's pretty good going.