Diana biopic Spencer wobbles between the bold and the bad

You may feel that you've had enough of Princess Diana's story on the big and small screens, what with Naomi Watts taking the role in Oliver Hirschbiegel's awful Diana in 2013, and then Emma Corrin playing her in the most recent season of The Crown, with the mantel set to be passed in Elizabeth Debicki in the next run. But, to give it its due, Pablo Larraín's Spencer marks the only time the People's Princess has been shown delivering a lecture on Anne Boleyn to an old coat that she has just stolen off a scarecrow, and then having a chat with the ghost of Boleyn herself shortly afterwards. The Chilean director doesn't go in for conventional biopics, as anyone who has seen Jackie (starring Natalie Portman) or Neruda will know. And here again he has gone for a surreal portrait of his iconic subject. The snag is that his experimental art house spirit keeps bumping up against the naffness and the familiarity of British films set in stately homes, so his psychodrama ends up being both ground-breaking and rib-tickling.

It's set over three days in 1991, from Christmas Eve to Boxing Day, at Sandringham House in Norfolk. The rest of the Royal Family has arrived for their holiday in a fleet of chauffeur-driven cars, but Diana (Kristen Stewart) rocks up on her own in a Porsche convertible, having taken a detour to visit the aforementioned scarecrow: her dilapidated childhood home, from the days when she was Lady Diana Spencer, is a field or two away from Sandringham. Her late arrival concerns the sympathetic head chef (Sean Harris) and bothers the Scottish army veteran (Timothy Spall) who has the job of ensuring that everything goes the way the Queen wants it to. Her Majesty's insufferable Christmas traditions include weighing all the guests when they arrive and when they leave to ensure that they've been sufficiently gluttonous. But Diana is in no mood for festive japes. Her Christmas present from Charles (Jack Farthing) – a necklace with pearls the size of golf balls – is identical to the one he has given his mistress. And the whisper in the servants' quarters is that the Princess is "cracking up". The filmmakers apparently agree.

Steering away from the same territory as The Crown, Larraín and Knight don't fill the film with awkward meals and heated arguments (although there are one of each of those). Prince Charles does some grumbling, but the Queen has hardly any lines and Prince Philip has none: they are closer to menacing waxworks than people. For most of the time, Diana is either talking to her young sons, her trusted personal dresser (Sally Hawkins) or to herself. It's interesting, this lack of dramatic conflict and discernible plot, but it can leave the film seeming as listless and purposeless as Larraín's Diana herself. Her favourite occupation is to wander around the estate until she finds something that has an ominous symbolic connection to her, and then make an unconvincing speech about it. Ah, pheasants! So beautiful, yet bred to be killed!

Spencer is a folly that wobbles between the bold and the bad, the disturbingly gothic and the just plain silly

Stewart is such inspired casting that she makes all this eccentric nonsense watchable. She's been practising Diana's signature moves for years – dipped head, hunched shoulders – and she certainly knows what it's like to put up with intrusive tabloid photographers. She also looks suitably fabulous in the many outfits that Diana is required to wear over the long weekend. And unlike Watts's performance in 2013, hers doesn't seem distractingly like an impersonation. Mind you, she delivers all her lines in little bursts of hissing whispers, so if you don't see it with English subtitles, as its first audiences did at the Venice Film Festival, you might not understand more than half of what she says.

The effect is a bit odd, but there are lots of odd things in the film, not least the tone and the pacing, which lurch around like someone who's had too much after-dinner port. Between Jonny Greenwood's squalling jazz soundtrack, the hallucinations, and the blush-making sexual confessions, Spencer is a folly that wobbles between the bold and the bad, the disturbingly gothic and the just plain silly. In some scenes, it's heart-rending in its depiction of Diana's self-harm and bulimia. In others, it's almost as risible as the Diana biopic from 2013, and that's saying something. I didn't know any more about Diana afterwards than I did beforehand, but I can't say I didn't enjoy it. This is a film that echoes The Shining at the start and 2001: A Space Odyssey at the end. The Crown Christmas Special it ain't.