Lily Allen was turned away from a VIP area at Wireless festival on 3 July.
The 30 -year-old singer - who attended the festival with a group of friends - reportedly tried to enter the exclusive Live Nation area, where drinks were free, but was instead told she was not allowed inside by security, who claimed they did not know who she was.
Lily - who has daughters Ethel Mary, three, and Marnie Rose, two, with husband Sam Cooper - told security: "I don't want to make an unnecessary scene. Can you get someone from Live Nation to get me in?"
However, security guard Sarah refused to back down in the row, denying Lily access to the VIP area.
She told The Sun newspaper: "I don't know who Lily thinks she is, but she's not getting past me.
"She was coming out with the lines but they weren't working. She had to walk away with her tail between her legs."
The incident at Wireless came a week after Lily collapsed at Glastonbury festival.
The 'Hard Out Here' singer reportedly fell to the floor near the Silver Hayes dance area and had to be treated by paramedics.
An eyewitness said: "She went outside to sit down on the grass. Gradually, she bent over, then slid forward to lie face-down in the filthy grass.
"She was out of it, she didn't know where she was. Her friends were saying, 'You all right?' and trying to give her water.
"Her eyes were rolling and her chin was moving from side to side, chewing constantly."
Bang Showbiz