Lily Allen broke down mid-show after witnessing a fight last night (07.03.10).

The 'Not Fair' singer was horrified by the brawl in the crowd at London's O2 Arena and left the stage in tears as security escorted the middle-aged men out.

Upon her return, she said: "That's the worst sort of violence. It's f***ing sick and you lot should be ashamed of yourself."

However, controversial Lily did not end the night on a low point, and dedicated her expletive-filled song 'F**k You' to Conservative Party leader David Cameron, who last month declared her music unsuitable for children.

She said: "I'd like to dedicate this next song to someone. David Cameron."

The 24-year-old star was playing one of her last performances before her retirement from music - she plans to set up a vintage clothes shop and launch a record label.

Lily recently revealed she wanted to take a break from music for five years, saying: "I'm just doing a different job for a bit. I'm having a career change. I just want to stay in London for a while. It's not a particularly healthy lifestyle being on the road."