Relatives of the man injured in an apparently unprovoked attack at the Pulse nightclub near Blackfriars Bridge early on Wednesday morning are at his bedside as he remains in a critical condition in an east London hospital.
The victim, a 37-year-old telecommunications professional from Lancashire, was attending a party at the Pulse nightclub hosted by the makers of Blackberry smartphones to promote their BBM instant message service.
Detectives believe the assault was unprovoked and that the man is an innocent victim of a violent attack in which he was struck with a bottle.
It is thought that the rapid response of staff at Pulse, who administered first aid, saved the man's life.
A 25-year-old man was detained by club staff and subsequently arrested by officers. He remains in custody at a south London police station.
"The investigation team are aware that a number of potential witnesses to the events immediately prior to, during and after the incident were in the bar area of the club at the time," said a police spokesman.
"An incident room has been opened under Detective Chief Inspector Cliff Lyons of the homicide and serious crime command at Lewisham Police Station.
"We would urge anyone with information that could help the investigation to contact the incident room on 020 8721 4961."