The subtitle of this biography alludes to a line from Hardy that Thom Gunn used as the epigraph for his last collection, Boss Cupid: “Well, it’s a cool queer tale.” Gunn’s life was cool and queer in the way that we use those epithets now; his poetry was cool and queer in the way that Hardy used them.

His breakthrough poems in the 1950s were all Elvis, Brando and biker gangs in content; but existentialist in preoccupation and rigorously Elizabethan in form. He was a very old‑fashioned modern. After FR Leavis, his great critical father figure was the austerely tweedy Yvor Winters. His lodestars were Ezra Pound, John Donne, Thomas Wyatt and Stendhal. In his life and in his work he sought control, panache, a willed stance to meet the world.

He had a lot to hold together. The only woman who had any real significance in his life was his mother. She killed herself when Thom was 15 and his brother 12, and Thom found the body. It wasn’t until 1991, in The Gas Poker, that he wrote about his mother’s death – and was only able to make the poem work when he shifted to the third person. He found a talkier and more personal voice, on and off, from the 90s onward, but he was still guarded.

Gunn’s lifelong warmth and cheerfulness, his determination to have a good time, emerge in Michael Nott’s sensitive telling like a sort of carapace: a coolness disguised as its opposite. On the face of it, his life should make a hell of a story. He had a ton of sex, took a ton of drugs, lived through the Haight-Ashbury 60s, the 70s San Francisco gay scene and its 80s Aids epidemic. His collection The Man with Night Sweats, along with Tony Kushner’s Angels in America, was the outstanding literary response to that crisis. He was a keen critic and, when on song, one of the best poets of his generation in the language.

But there’s less incident than you might think. He was sexually promiscuous but romantically almost completely monogamous. He and the American Mike Kitay met at Cambridge pre-Wolfenden, when both were in their very early 20s. They were each other’s first. Thom followed Mike back to the US, and though the sex fizzled out they were together for the rest of his life. In their big house in San Francisco they gathered a loving, unconventional, elective family of gay men.

Gunn’s outlook didn’t seem to change much – not, at least, till his poignant last few years. Poetry left him for good as he became properly addicted to speed and miserable about entering old age. His relationships with his Cole Street family frayed. He paraded ever less suitable and more exploitative sexual partners through the house, knowing that three-day chemsex sessions with light-fingered junkies probably weren’t advisable for a man in his mid-70s with high blood pressure, but he was apparently past caring. In 2004 the inevitable happened. “Acute polysubstance abuse” was the coroner’s verdict.

Michael Nott has produced a consummately researched, intelligent and sympathetic biography – and, which matters most, he’s a very good reader of the poems – but it’s a bit overdutiful. Everything you want is in there; so is a lot you probably don’t. It’s about 200 pages too long, and many of those pages are month-by-month descriptions of not much happening, or fastidious accounts of changes in the decor or bar staff of the second-best pickup joint in the Castro. Events are unfailingly glossed with quotations from diaries or letters or interviews: “he remembered”, “he recalled” or (incessantly; sometimes twice on the same page), “he reflected”.

Whole decades seem to pass with Gunn fretting, being blocked, then writing a few poems, then being blocked again; moving from free verse to form and back again; teaching (which he did excellently); fretting about his relationship with Mike; hitting the leather bars for tricks; taking drugs (tracking the zeitgeist, acid gave way to snorting speed and taking MDA, gave way to injecting speed, with dabblings in crack and heroin); fretting.

But there are plenty of funny and poignant bits, too. He gives Elizabeth Bishop a joint (“She puffed it manfully”). He seeks to restrain his bereaved, PCP-crazed housemate from hurtling down a rainy street in his carpet slippers “to meet Jim’s astral projection”. Invited to lunch at a Pall Mall club he shows up in full leather gear and scandalises the members. On an early visit to New York, the two poles of his existence clash when he’s offered a job in “a tough-queer bar”; he would have taken it “if he hadn’t already signed this damn contract” with Harvard.

And for all the frantic cruising and shooting up, the sad ending, one image that stays with you is of this lovable and conscientious man at home with his homemade family, cooking his terrible meatloaf: “fastidious, methodical and quietly determined, and a bit fussy: sober, spectacles resting on the tip of his nose, recipe book open at the appropriate page, stirring grimly away, eyes on the clock”.