Nancy (Emma Thompson) is brutally aware of her status as an unfulfilled woman and in a moment of daring hires a sex worker to be her undercovers coach. In walks the splendidly named Leo Grande (Daryl McCormack) – tall, gorgeous and comfortable in his perfectly proportioned body.

What follows is a comedy of sexual manners set almost entirely in the nondescript hotel room Nancy hires for their encounters, and the film needed a deft touch. It could have been too fairytale or patronising; worse, it could have been dull. Sophie Hyde is getting international notice for the edge she brings to the screen, and here she delivers a wryly amusing film with a radical message about bodies, sex and freedom that has generated considerable comment (the film premiered at this year’s Sundance Film Festival).

The casting of charismatic Irish actor McCormack (Peaky Blinders) is the perfect foil for Thompson’s Nancy, who is awkward and self-deprecating. Unlike her, Leo is at ease with the circumstances of having sex with a stranger. She nervously lists a series of positions she wants to try out. “I think we’ll make a significant dent in this,” he says, as if she just ordered new curtains.

The trajectory is predictable but how it gets there is not. Thompson gives a captivating, bravura performance as a woman discovering her sexuality and McCormack meets her at every step with not just charm but tenderness. Hyde works hard to keep things fresh and doesn’t linger too long in places where the camera doesn’t need to be. So, while it is a film about sex, it is until the last part surprisingly chaste when it comes to their actual encounters.

Of course, the question comes up of who Nancy and Leo both are, and a misstep by Nancy almost derails their sweet and intimate friendship. It also brings about a tonal shift that isn’t entirely convincing, with Leo storming out in anger after Nancy crosses a boundary, then showing a surprising quickness to forgive. Good luck to you, Leo Grande, for that.

Care was taken to maintain the comfort and security of the actors on set, and the inclusion of a scene at the end where Nancy appraises her nakedness stayed in at Thompson’s request. Behind the gaze is a newfound confidence that her body can give and receive pleasure. Of course, we are watching Nancy, but we are looking at Emma Thompson and it’s a breathtaking moment of courage and conviction that nails the film’s serious intent.

Good Luck to You, Leo Grande is in cinemas now.