The middle class girl, from a theatrical family in Surrey, will have won countless new admirers and they won’t have to wait long to see her again.

Since graduating from the Guildhall School of Music and Drama in 2010, she has notched up an impressive list of acting credits.

Last year she was seen in another racy role in the ITV drama: Secret Diary of a call Girl opposite the actress Billie Piper, 29.

Born in Surrey, her grandmother Helen Horton was an actress who had roles in Alien and Superman 3, and her father was also an actor, although he died from cancer in 2000. As a child she attended the ￡21,000 a year Arts Educational School in Tring, which counts actresses Jane Seymour, Julien Andrews and Thandie Newton amongst its alumni.

Barely out of drama school, she won the role of Ethel, William Brown’s coquettish older sister in the BBC adaptation of Richmal Crompton’s Just William stories in 2010. Then followed a starring turn in the British film- Fast Girls.

Having been ‘optioned’ for series four of Downton Abbey, Miss James will next be seen in the Christmas special. In her role as Lady Rose, the great niece of Maggie Smith’s character, the Dowager Countess of Grantham, she is the ultimate femme fatale who throws the world of Downton into disarray.

Speaking in an interview earlier this year about the role, the actress hinted that she is often cast as posh young girls. Describing her turn as Lady Rose, she said: ‘I come in at the end and I am playing a posh person, surprise, surprise’.