It is a tale of seething jealousies and violent passions – but it is one rapidly in danger of being matched by the real-life dramas of its leading actors.

When The Edge Of Love opens later this month, it will do so amid fevered speculation that the on-set closeness of two of its stars, Matthew Rhys and Sienna Miller, was the
catalyst for the end of Sienna’s year-long romance with actor Rhys Ifans.

On the town: Sienna Miller and Matthew Rhys at a showbiz function last year

Certainly the chemistry between the two as they take on the roles of Dylan and Caitlin Thomas at one of the most volatile periods of their marriage is undisguisable.

But while that on-screen frisson may bode well for the film’s success, it seems to have done for Sienna’s relationship with Ifans.

Last week, it was reported that the couple had split when Sienna, tired of Ifans’s jealousy and suspicion, called a halt to the relationship that once looked destined to end in marriage.

On location: Rhys and Miller in their roles as Dylan Thomas and wife Caitlin

Ifans, 40 this year, is understood to have been unhappy at the amount of time that Sienna, 26, was spending with Matthew, 33, during increasingly frequent visits to Los Angeles to prepare for the film’s promotional campaign.

The pair have been seen dining out together in LA several times and, while they deny any romance, Ifans’s unease was heightened by the fact that Sienna had dated Matthew up to the time when Ifans and she became a couple last summer.

Ifans – best known for his role as Hugh Grant’s flatmate Spike in Notting Hill – is a successful actor and popular man, famous for his wild-living, natural charm and haphazard approach to personal grooming.

Happier times: Rhys and Sienna strolling hand in hand in West London last month

But he was branded a ‘traitor’ by Matthew and Fantastic Four star Ioan Gruffudd – fellow members of the Hollywood ‘Taffia’ – when he and Sienna got together. Until then, the three men had been firm friends.

Such conflicts of love and friendship also lie at the heart of The Edge Of Love. The film focuses on an infamous event in 1945 when the Welsh poet was said to have been shot at by the husband of Dylan’s first love – Vera Killick.

Keira Knightley plays the glamorous former dancer turned singer Vera. Keira, 23, was originally cast in the role of Caitlin but opted for the more sexy character of Vera.

In its depiction of overlapping affairs and hedonistic creativity, the story of Dylan, Caitlin and Vera could rival anything that London’s louche Primrose Hill set, on whose edges Sienna existed thanks to her relationship with Ifans, has to offer.

The plot chronicles the time, shortly after the birth of Dylan and Caitlin’s daughter, Aeronwy, when their marriage is in crisis in the face of his alcoholism and their mutual faithlessness.

Then Dylan has a chance meeting in London with childhood friend and former lover Vera Phillips and the die is cast.

Vera marries her fiance William Killick, played by Cillian Murphy, 32, but soon embarks on a torrid affair with Dylan.

It is complicated by the unlikely friendship that springs up between Vera and Caitlin – two women who should, after all, be total rivals.

As the film’s female leads, Sienna and Keira embrace the feisty, free-spirited characters of the women they portray.

The images of the girls – kicking about in their wellington boots, Forties cardigans, wrinkled stockings and woollen skirts – may appear carefree and innocent, but an undercurrent of lesbian lust underpins this depiction and adds another side to the love triangle.

When the betrayal is uncovered, Vera’s husband, a commando, launches his furious attack on Dylan. In reality, Killick was cleared by a jury of attempted murder, despite Dylan’s evidence about a gun attack.