Cert 15 Stars 5

There’s a startling power to this modern day horror which is powered by devilish intent and graced by an immaculate performance of subtle complexity by Swedish-born Welsh actress Morfydd Clark.

As a devout hospice nurse called Maud, Clark delivers a confessional, fragile, stern and punishing turn, yet always maintains our sympathy as she becomes infatuated with her latest patient, Amanda.

She’s a former dancer who’s now wheelchair bound and in need of palliative care, a role which requires a great deal of intimacy and includes bathing, physical therapy and massage.

You’ll remember BAFTA winning Actress Jennifer Ehle as Elizabeth Bennet in the 1995 BBC miniseries Pride and Prejudice opposite Colin Firth’s Mr Darcy, and she masterfully switches moods in a role requiring her to be sexy, self-pitying, abrasive and cruel.

Together they form a frighteningly intense double act, and their delicate relationship spirals out of control to jaw dropping and heartbreaking effect.

There are shades of One Flew Over the Cuckoo’s Nest’s Nurse Ratched in Maud, and there’s nothing more disturbing than bad behaviour carried out by those believing they are doing good. Especially when convinced it’s what the Lord wants them to do.

On her feature length debut, Rose Glass directs with the conviction of someone in possession of a terrific script. Which she is. And she wrote it, filling the screen with jealousy, rapture, blood, pain and cockroaches.

Cinematographer Ben Fordesman provides bleak exteriors and oppressive interiors, it’s edited with tight-as-a-drum economy by Mark Towns, and Adam Janota Bzowski’s tremendous music seems to bypass your ears and penetrate straight to your soul, combining to create an atmosphere foggy with sexual intrigue and dank with skin scrawling menace.

This is definitely not for the squeamish and watching it probably qualifies as a traumatic event. It is so suffocatingly great I barely breathed for the last half hour and was left exhausted from nervous tension. Saint Maud is the best British horror in years.