The closest thing London's Theatre Royal's probably ever got to exhibiting heavy metal is the galloping steel framework of the larger-than-life puppets in First World War tearjerker War Horse. Indeed, theatre land's foundations  are rarely rattled in quite the same way they are tonight, thanks to Swedish progressivists Opeth's (no strangers to raising the roof at royally appointed auditoriums) nigh-on three-hour onslaught of lofty, goth-y tech-metal. Obviously, your average well-heeled theatregoer is nowhere in sight. Instead the aisles are stuffed with a wire-haired, pasty mass of metallers who, it appears, have been surviving on a steady diet of Iron Maiden and bad lager for the last two decades.

While primarily celebrating the 10th anniversary of the release of their matricidal-of-concept eighth LP Ghost Reveries by riffing through it in its entirety, the band are also presumably aiming to prove to grim-faced cynics that they haven't gone completely soft since the release of 2011's retro-prog no-growl-zone, Heritage, an album that lost them a number of fans for its apparent lack of anything 'death'-related, be it riffs or otherwise.

Boasting ornate, wedding-cake tracery, the historic West End theatre, it turns out, is the perfect match for Mikael Åkerfeldt and co's darkly florid orchestrations.  The auditorium's rapier-sharp acoustics finely sculpt their rich, layered sound. Meanwhile, mirroring Ghost Reveries' spectral artwork, the stage is set with dripping gothic candelabras, dapples of wraithlike light conjuring a sense that we could just as well be attendants at some Eyes Wide Shut-like occult orgy.

However, the affable Åkerfeldt's – equal parts deadpan-comic and prog wizard – droll between-song banter instantly shatters this unhallowed illusion. "This is a royal theatre, right"? he quips at one point, concluding merrily with "cunt", all of which is met with uproarious laughter and applause.

As the show progresses, the frontman's good-humoured shine is partially eclipsed by certain baying, knuckled-headed factions of the audience, who think it's amusing to constantly heckle after every song, dumbly imploring the band to play the likes of "The Chillis" or "Taylor Swift".

Due presumably to their ambitious, defiant and virtuosic nature, the band does tend to attract obsessives and  trolls, a few of whom have seemingly crawled out of the woodwork  to humiliate the band. Åkerfeldt's poise and affability only lasts so long, and before launching into Ghost Reveries' glowering, penultimate dirge 'The Grand Conjuration', he testily orders an anonymous catcaller to "shut the fuck up, motherfucker".

Despite the baiting and crowd-participation fuckery, the main event is mostly absorbing, fearsome and strangely uplifting, if at times exhausting. In the first set, the monstrous one-two of 'Ghost Of Perdition' and 'The Baying Of The Hounds' has the VIP boxes quaking, while an extended 'Atonement', with its lashings of star-spangled guitar and organ soloing, is a mesmerising signpost of their more recent albums Heritage and Pale Communion.

Despite having been panned by some critics and fans for their supposed musical about-face (from technical death metal to jazz-tinged prog). It's clear tracks like the serpentine, classical-guitar spangled 'Reverie/Harlequin Forest' share much in common with more ethereal cuts like 'Eternal Rains Will Come' and 'I Feel The Dark'. While on the surface the latter songs exude a lighter atmosphere, they still churn below with all the menace of the older material.

In terms of quality, though, their latest tracks probably don't quite reach the high-water mark of their early period not because the shortage of blood-curdling screaming or malevolent riffing, but because they're not as tightly focused. The winding, seemingly directionless 'Eternal Rains Will Come', for example, sounds like a half-baked outtake from Gentle Giant's The Power and the Glory.   Never mind the negatives though, Opeth are everything a modern prog-metal band ought to be: at once spellbinding, perplexing and faintly ludicrous.