Justin Bieber reveals new 'mature' direction as Biebermania hits London

They stalked him from Heathrow to his Kensington hotel, one hyperventilating mass of phone-wielding, TwitPic-posting, pubescent shrieking as the Justin Bieber circus hit town.

But his army of Beliebers could be in for a shock as the teen singing sensation used his London visit to unveil a new “mature” direction.

Few pop stars attract the hysteria surrounding the Canadian, 18, who boasts 20 million Twitter followers (rising by one every other second), 8 million sales for his breathily-delivered songs of devotion and rabid scrutiny of his romantic entanglements.

Dispatching Theresa May with a sideways Tweet after immigration delays at Heathrow (“Airport was crazy…Some people always tryna ruin it for the fans”), Bieber teased the gauntlet of screaming girls with a hotel window flash of his “six-pack” chest.

However Bieber faced a more sceptical audience when he invited the European media to a swanky Ladbroke Grove club to sample his new album Believe, a crucial step in the plan to turn the singer, discovered posting R&B cover versions on YouTube, into a serious artist in his own right.

The security surrounding this masterpiece suggested the discovery of a lost album of Beatles originals. Mobile phones were surrendered. But also Dictaphones, bags, coats, jackets, hats and scarves, anything that might conceal a recording device. Pens were checked for pinhole cameras. Once inside, every journalist received a Bieber book, its every page a blank sheet.

The man himself leaped on stage, to an ear-splitting chorus of “Justin!” from 12 barely-believing Beliebers, plucked from the bedraggled crowd pleading for entry outside.

“I really appreciate you giving me your ears,” said Bieber, rebooting Shakespeare’s Mark Antony speech, before delivering the big news – he is growing up.

Describing new song, All Around The World, written with R&B producer Rodney Jerkins, Bieber said: “We wanted something more mature. I’ve grown up and I’m making music that I can relate to and older people can relate to too. I don’t want to lose my young fans but I want to grow the audience.”

A much-derided album of Christmas songs was released last year “to get them used to my new voice.” He has co-written all the songs on the record, including one performed solo with just an acoustic guitar accompaniment. “It sounds like a mix between Fergie (the Black Eyed Peas singer) and Jesus,” he boasts.

Sex and paternity suits? That’s on the menu too. “I’m going to be talking about everything I’m going through,” said Bieber, who is in a relationship with Hollywood actress Selena Gomez. “I've written a song about that whole situation with that girl who said she’s having my baby (Mariah Yeater, who withdrew the false claim).”

Bieber frequently sought guidance from the man above, not God, who was praised liberally but Scooter Braun, the manager who has guided the phenomenon since discovering the singer on YouTube and is watching proceedings from a VIP balcony.

Excited about his new collaborations with Kanye West and Drake, Bieber asks Scooter if he can play unfinished tracks from the album and is told that he can’t.

Mainly Bieber is like any teenager – he wants to play his music really loud and gets frustrated when he’s told he can’t. “Turn it up,” he appeals as the room shakes to another new “club banger”.

The songs become submerged under a fuzzy distortion. “The quality is so bad, it’s not supposed to be like that,” he complains, in a rare show of steel behind the doe-eyes.

His entourage of minders and record company marketeers look aghast. “It’s going to reflect on my song and it should sound better than that.” An engineer is dispatched as the PA system emits a huge bang and judders to a halt.

With a gap in proceedings, questioner Reggie Yates steers Bieber back on to the subject of girls. “Girls like more than gifts. A picnic – girls love that stuff,” the heartthrob said, prompting more shrieks from the back of the room. “But sometimes they give you a headache.”