Robbie Williams is, as Keith Richards said of Mick Jagger, “a great bunch of guys”. I have just spent the afternoon with several people, most of them Robbie Williams. He has veered from stand-up comic to psychic investigator, to half-helpless boy being helped into his shirt by his PA. He’s improvised a song on his guitar (“Blue on blue/ Living alone"), solicitously proffered vitamin drinks, sternly called for Prohibition in Britain (“ Everyone here fights — we’re not jolly drunks, like the Scandinavians”), made the lyrics of Je T’aime (Moi Non Plus) ruder, and threatened to rip his ex-manager’s uterus out, despite his ex-manager being a 47-year-old man called Nigel.

He has even explained how he was supposed to duet at the Brits last year with Morrissey, on a Morrissey song called I Like You (“I like you/ But it’s so shameful to me/ You are not right in the head”). The performance was to have concluded with Morrissey and Williams kissing, “like Britney and Madonna on the MTV Awards”.

Alas, in a flurry of confusion and politicking, the whole thing fell through, and Williams ended up duetting with Joss Stone, instead, who didn’t kiss him at all.

During all this, Williams has generally been “up” Robbie. And “up” Robbie is very pleasant. He asks you questions — even if one of them is “So you’ve had two kids? Is it like a wizard’s sleeve down there, then?”

As we make our way over to his MTV interview, however, for reasons unknown “up” Robbie gradually appears to sink. By the time he’s sitting in a large armchair, arc-light shining in his face, MTV at the ready, he appears to have gone through the emotional equivalent of a testicle withdrawing into the body due to inclement weather.

The interview is one of the more uncomfortable things I have had to watch in the name of light entertainment. The interviewer — an unexpectedly besuited man who appears to be moonlighting from QVC — clearly believed that half an hour with Robbie “Let Me Entertain You” Williams would be a doddle. Five minutes in, it’s clear it won’t be.

“There’s a long, very atmospheric fade-out to King of Bloke and Bird, the last track on the new album,” MTV guy says. “How did that come about?” “I knew nothing about it,” Williams says, looking detached. “You’d have to ask Steve (Duffy, his musical collaborator) about it.”

“There's a real Stonesy feel to A Place to Crash," MTV guy suggests.

“Well, Steve knows about that,” Williams bats the question away. “He has every song the Stones ever recorded.”

“We need to ask you some questions about Bob Geldof.” MTV guy is sweating quite by badly now. “How has Bob Geldof changed the world?” “I don’t know, really,” Rob says. “I don’t know him, and I don’t know much about his work. I’m sorry, but that’s my truth, and that’s all I can say.”

The cumulative effect is of Robbie Williams as a bored pop dilettante. This is directly at odds with what Williams has spent half the afternoon ranting about to me — that the biggest secret in the music industry is that Robbie Williams is passionate about music. He is, after all, the man who has the opening bars to the Beatles’ All You Need is Love tattooed across his back. He even opened up his iTunes and played unreleased demos from the last album, pointing out where he’d “borrowed” inspiration and, indeed, whole hook-lines.

As soon as the MTV interview finishes, however, Williams is back to his ebullient self. Best friend Jonathan Wilkes has turned up, wearing a new hat. Debate on the subject of the hat takes the best part of five minutes. Robbie is unconvinced about the hat. Wilkes is passionate about the hat. Then Wilkes starts to feel too hot. There is talk about what a warm autumn it is turning out to be. They decide to go for kebabs. Work is over.

The first time I interviewed Robbie Williams he was a great bunch of guys, too. It was 1997 — after the debut solo single, Freedom, but before Angels, before rehab, before people had stopped calling him “Robbie from Take That”. Asked to write his press biography by his management company, I went to its offices to interview him. “We’re trying to keep Rob off the drink,” they said. “Try to keep him in the office.”

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