Several audience members didn't bother to return after the interval, and there were a few walkouts even before that. It seems Christopher Alden's darkly brilliant new production isn't for everybody. But those of us who stuck it out for the full three hours were rewarded with a reminder that beneath the surface of the Shakespeare-based fairy fable lurk some disquieting truths.

Alden' s slow-moving but compelling reworking links so closely to events and themes in the composer's own life that it really becomes Benjamin Britten's own midsummer night's dream. There's no dingly dell, no enchanted bower.

Instead, Alden picks up on Britten's lifelong fixation with his own childhood and his Jacko-like penchant for the company of young boys. In Charles Edwards' realistically-detailed set, grim grey Victorian walls and barred windows loom over a school playground, with a bold 'Boys' sign above the door. (Later the Queen's portrait is hung above the boys' entrance while it's surrounded by fairies, if anyone still needs a hint). Sue Willmington's costumes make it clear we are in the late '50s, the time when the opera was written.

At first I was puzzled by the silent, lanky figure hugging the walls. Reading the programme during the interval revealed that "on the eve of his wedding, a man returns to his old school. Long-forgotten memories of his schooldays come back to him in the form of a dream". This troubled figure is Theseus (Paul Whelan, utterly compelling), who normally appears only briefly in the final act.

Puck, a teenage schoolboy (played by Jamie Manton), becomes the young Theseus. Oberon is a sinister, preying schoolmaster whose affections have switched from the growing Puck to the younger Changeling boy, just as the adult Britten callously broke with his devoted boy companions when the bloom of childhood began to fade. But first Oberon must pry the boy from the tweedy, twitchy Tytania, whose instincts may be protective or possessive, it's never quite clear. Theseus must somehow work through his own feelings, of despoliation, perhaps, or even misplaced guilt, so that he can free himself of the burden of memories before he marries.

The creepy paedophilic undertones contrast with the carefree snogging and fumbling of the slightly older schoolkids Lysander and Hermia, and Helena and Demetrius - in a way the real innocents, uncorrupted by the predatory desires of adults.

In Shakespeare's play the world turns upside down, and Alden shakes it up even further. The boys' chorus, normally a minor element, are naturally brought to the fore, a constant presence as they hang from windows or fill the playground, and, finally, set the school on fire, 'If'-style.

But the 'Mechanicals' (here, school caretakers and labourers) make less impact than usual. They don't quite fit neatly into Alden's concept. So when the 'love juice' is replaced by a moment of reefer madness, and Bottom's transformation into a donkey is awkwardly skimmed over, it all feels a bit forced. The mustard and ketchup palette of their final act play-within-the-play is as violent as its theatricality and as vivid as the parodic Italian-style music Britten supplies it with. Even though the singers milk it for all it's worth, the brief minutes of comedy come as a relief after the darkness. As Bottom, Sir Willard White revealed an unexpected gift for comedy. The rest of the Mechanicals were less subtle but no less effective.

Although the material is inherently short on dramatic momentum, Alden is never tempted to pep things up by cluttering the stage with superfluous action. Like Britten's sparely-textured music, where every note has a purpose, each scene focuses tightly on its subject. The drawback is a lack of spectacle, but the strength is that you really listen to the music, played with austere precision under the baton of the rising young conductor Leo Hussain.

The scheduled Oberon, Iestyn Davies, fell ill just hours before the opening night performance, so he walked his role while William Towers sang it expertly from the wings. Allan Clayton (Lysander) was also announced as ill (after kissing a badger, if you can believe his own Twitter feed), but he sounded perfectly fine to me, as did Benedict Nelson (Demetrius), Kate Valentine (Helena) and Tamara Gura (Hermia). All four were convincing as schoolkids and as the adult play-watchers they transformed into for the final act. Anna Christy made easy work of Tytania's butterfly coloratura, though she sounded in thinner voice than usual.

The boldness of this production won't satisfy all tastes, nor will its head-on engagement with Britten's personal psychology and sometimes distasteful motivations. If you want to sit back and let the music wash over you, look elsewhere for your thrills. But it turns an opera often dismissed as a featherweight into a profoundly disturbing examination of human desire.