"Police sources" quoted in the tabloids yesterday said that Liam was stopped in Oxford Street at 7.25 on Saturday morning by policemen who saw "an unkempt man obviously the worse for wear". The police are now testing the contents of two packages and Liam, released on bail, is due to return to the police station on 30 December.
The singer, now 24, has conformed perfectly to rock-star type so far, making millions, smashing up hotel rooms, moving in with a blonde starlet (herself a veteran pop wife), lunging at the paparazzi, fighting with his older brother and fellow Oasis member, Noel, vandalising music awards and flashing two fingers at the tabloid press.
As the editor of Music Week, Steve Redmond, comments: "I think it would be news if Liam wasn't arrested for possessing cocaine."
The brothers Gallagher have earned the devotion of millions for their homage to the music of the Beatles - some might say for ripping off the Fab Four and updating them for the Nineties - and, of course, John and Paul had well-documented brushes with the law over their fondness for illegal substances.
But where the Sixties' drug culture was mostly associated with attempting to expand one's mind, Liam is trying to anaesthetise his unhappiness and anger - or so says Oliver James, clinical psychologist with an interest in celebrity and its effects.
The Gallagher story, he says, is based on a childhood dealing with erratic parents who reacted inconsistently to bad behaviour, sometimes punishing it and sometimes laughing at it. Thus, the expression of anger or disapproval escalated constantly in a household where the young Gallaghers were self- confessed delinquents. After a while, Mr James says: "A shout no longer works, so you have to thump him, and then you have to thump him hard."
Life with Oasis, as described by their former road manager, Ian Robertson, in What's the Story? involves endless bickering punctuated by appalling rows, Mr James says. He quotes Noel: "How often do we argue? Every day, hourly," and the boys' mother, Peggy, who says fights between her sons "can start about the most trivial things". The defining point in Liam's life, Mr James maintains, came when he was 11 and saw Noel, then 17, thrashing their drunken, violent father, Thomas. Peggy and the boys moved out that day, and Liam became the apple of his mother's eye. "We were especially close," she has said, adding that Liam "wanted to be noticed", in contrast with his introspective brother (who writes the songs), Peggy adds that Liam "was never wrong - in his view, anyway".
Mr James adds that Liam's problems are compounded by Noel, whom the psychologist describes as intelligent but savage. He famously acknowledged that: "I will never forgive Liam for being born."
Questions about Liam elicit a sign of resignation from Capital Radio's Neil "Doctor" Fox. "The more people report it, the more he'll do it. He's only 24, he's got pounds 10 million in the bank, he thinks he can do what he likes," says the host of the Pepsi Chart Show, warning that those fans beyond the hard-core will soon be bored of his antics.
He also feels sorry for Liam (who never actually seems to enjoy anything he does). "None of us have any idea what sort of pressures there are on somebody like him. He's only a young guy and it's happened so quickly that one day he's going to come down to earth with a big bang."
Perhaps Liam wants only to shock; certainly in a world where no publicity is bad, Oasis has cornered a useful PR niche. His antipathy to Noel does seem to extend beyond the usual sibling rivalry; as Neil Fox points out: "That's why the music is so good".
To Steve Redmond, Liam is just enacting "classic rock-star behaviour", and he chastises the thirtysomething critics who complain of having seen it all before. "For the kids buying Oasis, he is the first one. They weren't around for the Beatles and the Stones. Liam is the original for them. That detached, critical mature view applied to Oasis is just irrelevent ... The fact he is not doing it for the first time is only important to people who are old and probably past it."
But which lesson of history will Liam follow? Mr James sees the likelihood of the singer committing suicide. An alternative model might be that he adopts an eastern mystic as guru, introduces non-traditional instruments to the next album, marries, has children and invites Hello! to his riverside mansion in Berkshire. Death of another kind for a man like Liam.