My gran got a shock in Tesco when she saw her priest, shuffling along behind his trolley in his black frock coat.

She was horrified to see the holy man buying novelty breakfast cereals and squinting at sell-by dates. Gone was his grandeur. No incense, no robes, no Latin - just Rice Krispies. She flinched at seeing him ordinary.

I felt the same when I opened this book, for I adore Morrissey. Like gran, I was reluctant to see my particular holy man in the cold light of day. I didn't want him to be revealed as someone who, dare I say it, puts Rice Krispies in his trolley.

I needn't have worried because this book has little to do with reality or common sense.

It starts as expected, with rich Dickensian description of damp, cobble-stoned Manchester. These passages could have been lifted from his finest songs, so sodden are they with melancholy and lyricism, speaking of how "Victorian knife-plunging Manchester … is the old fire wheezing its last".

Young Morrissey struggles to find a place in the macho working-class culture of the city but quickly realises music will save him. It is the "pale flash of glamour in our oh so pale lives" and he gives himself to it, utterly. He draws courage to be different, putting a streak in his hair, donning a blue satin jacket and worshipping Bowie, Bolan and the New York Dolls.

Forced to school each day, the teachers despise his hair and the albums tucked under his arm but he is set on his path and, through the revelation of music, sees himself as "a disfigured beast finally unchained from the ocean floor".

Devotees may spark up with tears at these passages, so beautiful and hopeful are they. There is humour, too. When a teacher fumes about Morrissey's audacity in being unhappy with "the hair colour given to you by Christ", he imagines being tended to in a salon, set under the dryer by Jesus, handed a magazine and asked if he's off anywhere nice.

But the book's brilliance wanes. Once he has found his way in life the heart drops out of the writing and instead we get bland factual statements such as: "I suggest to Johnny Marr that we call ourselves The Smiths and he agrees." In this soulless tone he describes the formation of the greatest band of the decade. Their luminous career is hurriedly got out of the way, and the infamous break-up is over in the blink of an eye. He seems to be speeding past this episode to press us along to something more important.

Finally, we realise what he is rushing us to and what the main focus of the book will be: not the formation of the artist, not the creation of magnificent music, but a court case where the former Smiths drummer, Mike Joyce, successfully sues for a bigger share of the band's royalties. Forty relentless pages are devoted to the tedious detail of the case. Not only are the legal aspects dull, but Morrissey appears bitter and resentful. Then, as we're hoping to leave the tiresome case behind, he presents us with a laborious deconstruction of every detail of the judgment. The book slumps under the onslaught of exhausting legal minutiae and Morrissey's relentless old-maid tetchiness.

This sagging segment of the book makes me wonder what the editor was thinking. Indeed, was there such a person, for the book's narrative is incredibly inconsistent. We are treated to pages of wit and poetry which often veer off into tiresome diatribes about global warming or the veal industry or the sinking of the Belgrano. Morrissey can't decide if he's a poet or a pamphleteer and there is seemingly no editor to guide him. The most crucial part of his story - The Smiths - is given relatively scant attention yet a massive portion is devoted to the court case. Towards the end, the book unravels completely into a series of near identical anecdotes about gigs he played in Denver, Gothenburg, Istanbul ... then you turn the page and it's blank. It seems the book is finished.

The absence of an editor was painfully clear as Morrissey often switches tense, stumbling from past to present, whilst there is an odd sprinkling of American spelling and idiom. His dialogue is written in italics and festooned with multiple exclamation marks, so that it reads like trashy Facebook-speak, with dollops of 'WHAT??!!' and 'Nooooo!!!' This is simply poor writing.

You could say I'm being harsh in focusing on the book's literary merit. It is, after all, a celeb autobiography, but the publisher has forced it under such scrutiny by releasing it as a Penguin Classic. That was a horrendous mistake if they weren't willing to edit it as such.

Compared to other celebrity-penned books, this one is superior but it is crying out for a ruthless editor. Morrissey is a magnificent poet within a three-minute song, but he can't maintain that throughout a 457-page tome, and certainly not without a sharp editor. (Oh publisher, so much to answer for.)

The book is too long, too patchy, too erratic and Penguin has done him, and us, a disservice.