The Minotaur, Royal Opera House, London<br />A Night at the Chinese Opera, Theatre Royal, Glasgow

A single chord of melody, twisted, truncated, transposed and inverted, winds through Harrison Birtwistle's latest and most terrible opera, The Minotaur. Like the scarlet thread given to Theseus by Ariadne, it leads us down from the desolate shoreline of Crete to the labyrinth where Asterios waits in a crude circus fouled with the blood of his victims. Caged in a body that cannot speak except in dreams, cursed by fate and nature, hot with rage and lust, he can do nothing but rape and kill until he too is killed.

Long on ugliness, short of redemptive beauty, rich with the rough, pungent poetry of David Harsent's libretto, Birtwistle's score is as violent as its subject. Bass drums rumble as the night sea boils and sucks; trumpets sound a futile distress signal; violins draw a faint skein of light across the sky; a flute sounds, naive and pure. Here, alone, is Ariadne (Christine Rice), watching the approach of a black-sailed Athenian ship, preparing the bowls of white paint with which the Innocents must daub their faces before descending to their deaths in a charnel house of clattering cimbalom and excoriating percussion. Toccatas puncture the drama like rusty blades; a masked chorus wails in excitement and impatience; memories of old transgressions buck and rear in blind, rhythmic patterns. Compared to this, Panic is a picnic.

Half-bull, half-man, half-brother to his betrayer and his murderer, the role of Asterios was made for John Tomlinson's weary bulk and baleful voice. The bull-shaped cage that covers his head and shoulders – made of wire mesh and lit from within – is one of many cages in the opera. Next is the gore-spattered amphitheatre, then the laddered labyrinth, then the shore: a barren circle sealed in Alison Chitty and Paul Pyant's spare, abstract designs with an eerie ring of blue and green light. Director Stephen Langridge uses naturalism and ritual as the Innocents (Rebecca Bottone, Pumeza Matshikiza, Wendy Dawn Thompson, Christopher Ainslie, Tim Mead) retreat to the darkened doors of the amphitheatre and return with blood bags to burst over their heads, throats, groins and torsos in choreographer Philippe Girardeau's whirling death dances. The anguish on their faces is almost too painful to watch; the sudden fold-down from fortissimo to pianissimo at the close of Act I is breathtaking.

As in most of Birtwistle's operas, individual characters are obliquely drawn. There is scant tenderness as the Minotaur and his half-sister curl into spoon-form to rest after the slaughter, scant attraction between Theseus (Johan Reuter) and Ariadne, for she is complicit in the violence. She watches without horror or pity as the Innocents are torn and tossed by Asterios, coming to life only as she talks of the past. Her spiteful, prurient, almost jealous description of her mother's brutal birth pangs and lust for the bull that was or was not Poseidon in disguise is one of the most disturbing monologues in the opera: an urgent, blatant, obscene, helter-skelter duet for crowing mezzo and gulping alto saxophone.

Why priapic Poseidon and Daedalus, architect of the labyrinth, escape censure is beyond me, but composer and librettist go further than most modern readers of this myth to suggest that greedy Pasiphaë and twice-used Aethra are to blame for their children's horrid lives. All the women here are red in tooth and claw. Literally so in the case of the shrieking Keres (led by Amanda Echalaz), whose dirty metal wings rake the floor as they tear out the hearts and lights and lungs of the dead. Hiereus (Philip Langridge) and the Snake-Priestess (Andrew Watts) – a counter-tenor Queen of the Night with varnished breasts like a ship's figurehead – offer little comfort. Armed and charmless, Theseus is simply an instrument of escape; the Minotaur's death is his price.

When it comes, it is no triumph, just another sacrifice to feed the bloodlust of the chorus, and, by extension, the audience.

Birtwistle and Harsent are not the first to present Asterios as a victim. In Steven Sherrill's novel The Minotaur Takes a Cigarette Break, we find him living in a trailer park in North Carolina, as locked in loneliness as he was 5,000 years before. In the novel, he dreams of the past in aphoristic verse. In the opera, sleep unlocks the words of torment and longing behind his grunts and bellows. Unless you rate Birtwistle more highly than Shostakovich, Wagner or Mussorgsky, it is not Tomlinson's greatest role. But the misery he communicates through the Minotaur's verbal and non-verbal sounds is profound. In the pit, Antonio Pappano treats Birtwistle's coagulated, jarring, bloody textures with as much refinement and passion as he brings to Strauss, Verdi, Wagner and Berg. Debut artists Echalaz and Bottone are stunning, the performances of Reuter, Rice and Tomlinson faultless. It's an awful, awful evening. But The Minotaur is an imperative.

Lee Blakeley's delicate, clear-eyed production of A Night at the Chinese Opera is a very different proposition. Where Birtwistle offers gore and misery on a grand scale, Judith Weir offers concision, wit, sorrow, a gentle warning not to mess with nature, and vocal lines that breathe easily. Thoughtfully cast, with Toby Stafford-Allen and Jane Harrington as Chao Sun and Little Moon, Damian Thantrey as their orphaned son Chao Lin, and Rebecca de Pont-Davies, Sarah Redgwick and Stephen Chaundry as the Actors who disrupt Chao Lin's successful career, A Night at the Chinese Opera is the finest ensemble piece Scottish Opera has produced since The Knot Garden. Scored in blocks of shimmering, sour-sweet colour, Weir's cool, bell-like instrumentation glows in conductor Siân Edwards's hands.

'The Minotaur' (020-7304 4000) to 3 May; 'A Night at the Chinese Opera' (0870 060 6647) to 22 May