The louche, addled aristocrat Patrick Melrose is dining in New York with Marianne, an old friend of a friend who doesn’t drink because it “dulls the senses and blurs the edges”. “Your point being?” Melrose replies. In the opening episode of this stunning five-part drama, adapted by David Nicholls from Edward St Aubyn’s semi-autobiographical novels, Melrose’s devotion to such dulling and blurring is made abundantly clear.

He’s in New York to collect the remains of his recently deceased father and although it’s immediately apparent that the relationship was uneasy, early intimations of family strife are no kind of preparation for what follows. In fact, the opening episode is often darkly comic. Melrose careered around the city in search of oblivion; swigging, snorting and shooting whatever liquids, powders and chemicals he can get his hands on. He isn’t a sympathetic character. Troubled but arrogant, he roams the streets protected by the kind of invisible force-field of entitlement that only inexhaustible piles of unearned wealth can construct.

At the heart of all this is an astonishing, perhaps career-best performance from Benedict Cumberbatch, who tweaks his jittery Sherlock persona, replacing brittle neurosis with a desperate, despairing wildness. In the second episode, the source of that despair becomes unbearably clear. Unblinkingly portraying the addict as an eight-year-old, it’s one of the bleakest hours of television you’ll ever watch.

Jennifer Jason Leigh and Sebastian Maltz in Patrick Melrose

Jennifer Jason Leigh and Sebastian Maltz in Patrick Melrose. Photograph: Justin Downing/Sky TV

Isolated and defenceless, in an almost reproachfully beautiful house in southern France, young Patrick (heartbreakingly brought to life by Sebastian Maltz) is a hostage to the malignance of his parents. His mother, Eleanor (Jennifer Jason Leigh), is bad enough – a selfish, negligent semi-alcoholic heiress mired in a pitiful blend of narcissism and self-loathing. But she’s positively saintly compared with her husband, David (a rebarbative Hugo Weaving), who is simply nightmarish; a physically, emotionally and sexually abusive monster. It’s harrowing; the claustrophobic parameters of Patrick’s world rendered agonisingly palpable. Repeatedly, he runs away only to find there is nowhere to go. Much like a relapsing addict, he simply covers and recovers the same hopeless terrain.

The trauma of these scenes aside, Patrick Melrose’s saving grace is, believe it or not, its humour. Melrose is horribly damaged but the show as a whole crackles and fizzes. It never feels worthy or preachy. And this, in a way, is of a piece with its central message. It is a tale of appalling, desperately unhappy rich people whose reflexive irony creates distance, whose sparkling wit disguises cruelty and whose status masks existential turmoil.

David Melrose and his friends are grotesque specimens of British upper-class dysfunction; people whose vulnerability has, via a few damn good thrashings and a stiff upper lip, curdled into sadism. His parenting strategy – and the pathetic wall of justification he constructs around his abuse – is that his boy needs toughening up. Patrick sometimes embodies many of these flaws, but unlike almost everyone around him, he is struggling, furiously and often unsuccessfully, to break through these destructive defences and deal with his pain.

As well as being a remarkable study of addiction, Patrick Melrose is full of wider resonances. It is a case study in the corrupting nature of privilege and an acute demonstration of how Britain’s upper classes nurture myths to obscure difficult truths. But Patrick wants to be a generational firebreak; the end of one story and the beginning of another, happier one. The Philip Larkin poem This Be the Verse (“They fuck you up, your mum and dad …”) is a recurring motif. But Patrick doesn’t accept the poem’s fatalism. He longs to become the father that his own never tried to be; the place where this awful cycle of abuse and sadness finally stops.

Any role model who prepares to collect his father’s remains with a quaalude binge must be regarded as flawed at best. All the same, Patrick Melrose makes for this year’s greatest television hero.