Eight years after Attack the Block, Joe Cornish returns to directing with an action-adventure epic for kids that updates Arthurian legend to the London suburbs with wit and bottomless charm. This nostalgic-for-the-80s tale of a 12-year-old boy who must defeat Arthur’s evil half-sister Morgana might leave you hankering for the edge or cult appeal of ATB, but the movie’s Tefal-coated optimism is 100% resistant to all forms of cynicism.

Andy Serkis’s son Louis plays Alex, a likable kid who’s running away from bullies when he pulls Arthur’s sword Excalibur out of a chunk of concrete on a building site. It takes the arrival of Merlin – ageing backwards, he’s a teenager in a duffel coat played by Angus Imrie – to explain that Alex must defeat Morgana and her army of undead demon knights. With his best mate Bedders, Alex gathers a crew of knights to save the Earth.

The movie plays as a kind of Tiddly Thrones, a gateway drug for kids into harder fantasy, though the so-so CGI is unlikely to scare even little ones. After Attack the Block, Cornish worked on scripts for Hollywood movies, but here his English sense of humour is back with a vengeance. In the film’s best gag Merlin frets: where in London can he find beaver urine and beetle blood for a potion? In the ingredients of a chicken-shop takeaway of course. And there’s some timely – probably coincidental – Brexit sniggers to be had as Morgana proclaims Britain “lost and leaderless”.

None of the young stars shine as John Boyega did in ATB, but this movie is sentimental in all the right places, and impossible to dislike.