Police are appealing for information after a man was stabbed with a broken bottle in the Leake Street tunnel below Waterloo Station on Sunday night.
The incident happened at around 10.15pm on Sunday 6 May.
The victim, a man aged 31, was inside The Vaults when an altercation occurred.
The man left the bar into the tunnel on Leake Street where he was attacked from behind and stabbed in the thigh with a broken bottle.
He was taken to hospital by friends and was treated for a stab wound. He remains in hospital receiving treatment. His condition is described as stable.
Investigating officer PC Rowe said: "This was an extremely violent assault leaving a man with a nasty injury requiring medical attention.
"We will not tolerate violence such as this and a number of detectives are working hard to establish who is responsible.
"I would ask anyone who saw what happened to get in touch as a matter of urgency, you might hold crucial information which could help us investigate."
Anyone who witnessed this assault is asked to contact BTP by sending a text to 61016 or by calling 0800 40 50 50 quoting reference 655 of 6 May. Alternatively, ring Crimestoppers anonymously on 0800 555 111.