Hard though it is to grasp the full extent of Paul McCartney’s wealth, this book showers you with gentle reminders. He once ordered a pizza to be flown from New York to London by Concorde. He sent a sick puppy on a 280-mile return journey by taxi to a vet in Glasgow, and made the same sort of provision for a duck with a broken leg. “Hundreds” of his cash-filled weekly pay packets were discovered at his house in 1967 but he was already so rich that he hadn’t bothered to open them. He had a yacht turned into a 24-track studio and converted a minesweeper to accommodate the band.

What’s more, he has several Magrittes and a circular bed that used to belong to Groucho Marx. He organised a display involving 25,000 flowers beside the M4 to advertise a Linda McCartney photo exhibition and gave his second wife, Heather Mills, a £360,000 annual allowance (almost £1,000 pocket money a day). If Pete Best, the sacked original Beatles drummer, got “about £8m” for playing on ten tracks on The Beatles Anthology, what sum would the band’s bassist have earned for co-writing most of its output?

But whenever you find yourself envying a life in which you could underwrite a $200,000 heart operation for a friend’s daughter, you remember the grim reality of such fame. McCartney is forced to erect ramparts of privacy to allow him even the ghost of a normal existence. He systematically purchased all of the land around his farm on the Mull of Kintyre, in Scotland, to create a vast, continuous exclusion zone. The wire fences and 65-foot observation tower at his Sussex retreat prompted neighbours to call it “Paulditz”.

His profile is such that he occasionally resorts to riding in vehicles with tinted windows and had to disguise himself in an afro wig to attend a George Harrison concert. Women claiming that he slept with them in the distant past file paternity suits: can you imagine the indignity of being asked to submit blood samples to disprove some pissed event that may or may not have taken place decades ago in a Hamburg Bierkeller?

The repercussions of his celebrity are colourfully examined in this detailed and engaging book, as are the chief figures in his life – his mother and father, his early girlfriends, John Lennon, Brian Epstein and his first two wives – but it is the changing nature of another relationship that makes the most gripping narrative: that of the subject and the author. Tough, fascinated, painstakingly thorough and studiedly unemotional, Philip Norman was always firmly in the Lennon camp, once declaring McCartney’s rival and professional partner to be “three-quarters” of the band. Norman’s bestselling Shout! The Beatles in Their Generation and his superb John Lennon: the Life make this abundantly clear.

But things have changed. The author’s stance has softened. First, McCartney gave his tacit approval for this book – “neither authorising it nor discouraging it” – which allowed Norman access to countless crucial, first-hand accounts. And second, a growing awareness and understanding of McCartney’s predicament both within and beyond the Beatles now allows Norman to excuse various characteristics that he once disliked or considered suspicious.

He accepts that McCartney developed his “double-thumbs-up” demeanour as a valuable public relations shield between the band and the ravenous world: somebody had to “be nice to the endless relays of boring, bombastic local dignitaries, officious police chiefs and dumbstruck, dumb-cluck journalists” and it is entirely to the bassist’s credit that he volunteered.

McCartney’s legendary charm now seems beguiling rather than offensive. It took serious powers of persuasion, Norman points out, to sell millions of copies of the syrupy “Mull of Kintyre” in the teeth of the punk revolution. Who wouldn’t want to be allowed through international borders when you’ve forgotten your passport? Who wouldn’t want to be able to hold the attention of a court of law with just the tiniest modifications of facial expression, after informing a judge that it was your “interest in horticulture” that had led you to possess the marijuana in the first place?

When a Lord of the Rings film project was mooted in 1968, McCartney was tellingly cast as Frodo Baggins, Ringo as Samwise Gamgee, George as Gandalf and Lennon as Gollum. On TV, Paul’s angelic looks made him “seem three-dimensional while the others remained flat”, an irresistible trait that let him conduct love affairs with two other women while officially stepping out with Jane Asher (the reason John and Yoko were initially inseparable, Norman suggests, was that Lennon didn’t dare to leave his new squeeze alone with McCartney, for fear that she might fall under his spell).

There is something attractive, too, about the notion that McCartney ended up being the sole Beatle with a firm grasp on the tiller. While George invited a troop of Hells Angels to hang out at the Apple office (where they harassed the female staff) and John sent spherical packages to meetings with the message “Listen to this balloon”, McCartney had the sixth sense to flag up concerns about employing Allen Klein as their manager, a deal from which they later paid a fortune to escape.

So why alarm bells didn’t ring when he ran into Heather Mills is a mystery that baffles even Philip Norman. At the time, friends advised McCartney (with excruciating irony) that taking up with this doughty campaigner would be like “walking into a minefield”. In selfless support of his new wife, he started to wear T-shirts bearing the slogan “NO LANDMINES!” when they used to scream: “GO VEGGIE!” There is something profoundly sad about the whole episode; it is a tale so unnerving and crammed with agonising incident that Norman devotes 80 pages to it.

Mills convinced the world – and her apparently suggestible new husband – that she was some kind of romantic rebel, who had run away from home as a teenager to work on funfairs, sleep rough in cardboard boxes and steal food from supermarkets. She was soon labelled a “fantasist”, revealed to be a former topless model and accused of pedalling untruths and exaggerations to the extent that Jonathan Ross declared that she was “a f***ing liar” and that he “wouldn’t be surprised if we found out she’s actually got two legs”. With her press profile switching from “Diana” to “Mucca” in a matter of weeks, she sued her exasperated husband for £125m and settled for £16.5m, which speak volumes in itself.

And what of the music? Very little of this book concerns McCartney’s songwriting, which is understandable, as it is the area so comprehensively explored by the great Beatles scholar Mark Lewisohn and by Ian MacDonald’s peerless Revolution in the Head – though when Norman describes Lennon’s and McCartney’s harmonies as “like vinegar and virgin olive oil”, you rather wish there was more of it. Instead, he is aiming to produce the most detailed composite picture imaginable and he succeeds effortlessly.

You’re left with a sense that McCartney’s life in the Beatles was impossible madness and that he has been in recovery ever since. “I was on the scrapheap,” he had thought, aged 27, when the band split up. “It was a barrelling, empty feeling that just rolled across my soul.” You’re so sympathetic that you want to forgive him everything.

Well, almost everything. He paid Wings members £70 a week and once deducted £40 for “hire of amplifier”.

Rock Stars Stole My Life! by Mark Ellen is published by Coronet