Two men were knocked unconscious and one was repeatedly kicked in the head after spilling a drink over a woman during a night out in Camden.
The kicked man needed facial reconstruction surgery and metal plates inserted in his cheek following the early morning assault, with police warning he could have been killed.
Detectives say the pair, 19, were talking to a woman underneath the blue Camden Town railway bridge on Chalk Farm Road when one accidentally spilt their drink on her.
Minutes later, they were confronted by a gang of six men, all aged in their 20s, who set upon them.
The pair were knocked to the floor and one was "kicked several times in the head", police say.
Detective Constable James Dillury, from Camden CID, said he particularly wanted the woman who spoke to the pair to come forward following the incident, which happened at around 1.30am on May 15.
He said: "This was an unprovoked attack on two men who were heading home.
"The level of violence shown by the suspects, who kicked a man as he lay immobile on the pavement is of grave concern, they could easily have killed him."
Anyone with information should call Camden CID on 101 or Crimestoppers on 0800 555 111.
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