*UPDATED* Most of today's outlets are, for some inexplicable reason, going with the not-at-all salacious headline "MAN STABBED IN NECK AT JESSIE J PARTY", which her reps are bound to be thrilled about. Troof of it is, it was a BlackBerry launch which she was hired to perform at.

The victim, believed to be in his 30s, is in a "serious condition" in hospital after being attacked with a broken bottle following the the singer's performance at a bash sponsored by BlackBerry at Pulse nightclub in London's Bankside Vaults last night.

Jessie - seen here aptly proffering peace signs as she left the venue - finished her set at around 11.40pm and guests were heading to the cloakrooms when a fight is believed to have broken out.

Benjamin Cohen, Channel 4's technology correspondent, was at the gig and says one of the door men got covered in blood.

Speaking with the Daily Telegraph, he said: "Everyone tried to leave at the same time but the organisers weren't geared up for it and there was a huge rush to get to the cloakroom. People were crying and quite a lot were being sick, whether from the blood or the alcohol... A lot of people here were teen users of BlackBerry who don't seem to have had a free drink before." Nightmare. Particularly for the non-drunk teenagers in attendance.

One man was arrested and is in police custody while the 450 revellers at the event were kept in the club until 1.50am while police launched their investigations.

At the time, a source told The Sun newspaper: "It happened in the main area to the right of the stage where the bar is after Jessie J had performed. VIP, celebs and everything cannot leave until cops get the statements they need. Everyone is really shocked."

Those who attended the launch include Sunday Girl, Zara Martin, Reggie Yates, Russell Kane, Greg James, Gabriella Cilmi, Jessica Jane Clement, Sarah-Jane Crawford, Tyrone Wood, Lisa Maffia, several dollied up randomers, Kerry Ellis, Chipmunk, Joey Essex, of course, and the most impressive fro in existence today.

UPDATE: WENN reports: "Witnesses told photographers that two men became involved in an argument, before one of them plunged a broken bottle into the other man's neck, causing life-threatening injuries. Jessie J was reportedly coming off stage at the time of the incident. Around seven police vans and two ambulances arrived at the venue and the injured man was taken out of the club on a stretcher, with blood pouring from his neck... Police later brought out a man in handcuffs, who was wearing a jacket over his head to protect his identity. Hundreds of people were reportedly prevented from leaving the area by security and police, who kettled them into an adjacent car park. People were seen screaming and shouting and even kicking down barriers in a bid to leave. The guests, which included The Only Way Is Essex stars Lydia Bright and Lauren Goodger, were questioned one at a time by a large group of police officers, before eventually being allowed to leave. The last of the guests eventually left at 2.30am."