She’s arrived in London from Guernsey, worried about a daughter who won’t answer the phone. He’s come from France to find a son he hasn’t seen since the boy was six in Africa. It is the time of the terrorist attack on London’s Undergound and buses, and the middle-aged English woman (Brenda Blethyn) and the elderly African (Sotigui Kouyate) have every reason to be worried. But they hardly take to each other. Pitched into a multiracial society far from the calmer, and whiter, waters of the Channel Isles, the woman discovers her daughter has been living with his son. And learning Arabic.

“The place is swarming with Muslims!” she complains. The African keeps his distance but knows they are in this together.

That’s the plot of French Algerian director Rachid Bouchareb’s small-scale but beautifully detailed film, and it contains a performance from Blethyn as the weepie, anxious mother that won her an ovation after the festival screening. She is magnificent, seeming to react rather than act and, without a false or sentimental note, managing to make us sympathise with her puzzled and anxious character. The dignified Kouyate is splendid, too, adding his own perfectly pitched performance.

Bouchareb’s portrait of London after the terrorist attacks is startlingly accurate and there’s a genuine feel for all of the players. Ken Loach couldn’t have done much better. This is a film no Londoner should miss: humane, stunningly acted, it will be a gross injustice if it doesn’t win a prize from Tilda Swinton’s Berlin jury.