The opening film of this year’s UK Jewish Film Festival is something special. Blending fact and speculation in the best traditions of the biopic, Ilan Duran Cohen’s The Jewish Cardinal is an intoxicating combination of ecclesiastical politics and very personal soul-searching, all bound into the indisputably real character of Jean-Marie Lustiger, the late Cardinal and Archbishop of Paris. Whether you’re interested in religion, or conflict, or just people, you’ll find something that chimes with you in The Jewish Cardinal.

In 1979, the priest of a wealthy Paris parish was named Bishop of Orléans by Pope John Paul II. Nothing unusual about that, surely – except that the new évêque, Jean-Marie Lustiger, had only joined the church aged 14. And before that he’d been called Aaron. The Jewish Cardinal joins Father Lustiger (Laurent Lucas) as he receives the shock news of his promotion, and it’s not long before the Catholic press exposes his upbringing in a family of Ashkenazi Jews who fled Poland for Paris before his birth. Devout (as, perhaps, only a convert can be) and convinced that his conversion was a deliberate act of God meant to bring together the Old and New Testaments, Lustiger decides to oppose the press and proclaim his Jewishness alongside his Christianity – regardless of the damage it’s doing to his already fractured relationship with his father (Henri Guybet). Lustiger senior loathes Poland and all its children, particularly John Paul II – who gave, in the year of his son’s investment as bishop, a controversial mass at the death camp which claimed his wife’s life.

However, Lustiger is a passionate supporter of John Paul II (Aurélien Recoing), who he meets repeatedly in the Vatican and at the papal retreat of Castel Gandolfo. On their first meeting, the Holy Father shows off his trainers, challenges Lustiger to a swimming race and gives him some tips on manipulating the media – Lustiger is smitten with the first truly modern head of the church. As Lustiger’s career continues to progress – from bishop to Archbishop, and thence to Cardinal – he builds on the Pope’s example and embraces modern communications, launching a Catholic radio station and embarking on a high-profile visit to Auschwitz despite its effects on what’s left of his family life. But when a renegade Polish cleric gives permission for a group of nuns to establish a convent in the abandoned death camp, Lustiger’s dual heritage finally turns and rends him with a vengeance. Will he be able to mediate between the obstinacy of his assumed church and the outrage of his birth faith? If he can’t, God knows nobody else can.

While it seemed necessary to give you a fairly substantial chunk of The Jewish Cardinal’s plot as context, the first thing to stress is that this is not an obsessively, piously accurate biopic. Director Ilan Duran Cohen instructed Lucas and Recoing to avoid aping their real-life characters, and – combined with the preponderance of scenes that take place behind closed doors, from Lustiger’s interactions with his family to his dinners with the Pope – the result is a film that feels free and accessible, showing both Lustiger and John Paul II as flawed, human figures more than capable of both attracting and infuriating an audience. Unsurprisingly, given its emphasis on uncritically adoring dead clergymen, the Roman Catholic Church hated the idea of the film and refused permission to film in any of Paris’ churches – every nave, altar and aisle in The Jewish Cardinal belongs, rather wonderfully, to one of a number of redressed Protestant churches.

But whether or not Holy Mother Church approves of this film, there is nothing for audiences to dislike. Duran Cohen, a Jewish director, handles both sides of Lustiger’s life with equal delicacy of touch, and Laurent Lucas is quite extraordinary as the fiery and quick-witted Lustiger, a man whose entire life was characterised by refusal to compromise. The highlights of the film are his interactions with his cousin Fanny (Audrey Dana), often his only real link with his family, and of course with the Pope himself. Decoing’s interpretation of the famously informal and subversive John Paul II is quite sensational, and despite his relatively low screen time he’s in danger of stealing the show – he is Hannibal Lecter to Lucas’ Clarice Starling, staying in one place and getting all the best lines while Lustiger runs around Europe in a flap. Although I should probably stress that no Pope has ever been proven to be a cannibal (yet).

Elsewhere, Duran Cohen observes the various unwritten rules of the biopic – make much of lingering close-ups, hammer home the family angle, keep the extra-diegetic soundtrack to a minimum – to generally astonishing effect, doing much with very little (although this film was shot for TV, there’s no corresponding drop in production values). I was reminded, both in the subject matter and in the oddly translated title (The Jewish Cardinal was released in France as Le Métis de Dieu), of the superb 2010 film Des Hommes et des Dieux, released in England not as Of Men and Gods but, curiously, as Of Gods and Men. In both films, the characters’ religious vocation is entirely secondary to their motivations and actions as humans – something that, as a name, The Mixed Child of God gets across much better than The Jewish Cardinal. When I met Duran Cohen last week (interview coming soon), I asked him about the change of title. “I thought of it,” he replied, daring me to argue. “It’s the fault of your language. What should I have done, called it God’s Mulatto?” In a sentence, this sums up the urge to entertain, adapt and clarify that makes The Jewish Cardinal such a perfectly wrought film. Be you Christian, Jew, both or neither, chances are it’ll teach you something worth knowing.