The incident took place in one of half-a-dozen unisex portable toilets lined up on the far side of the stage, on the Spa side.

The mum said: "It's every mother's worst nightmare. I'm really angry. My daughter's just been absolutely destroyed by this.

"It's destroyed her life and the lives of anyone around her. At the moment she's bearing up as well as can be expected – but who knows what effect it will have in the future?

"Out of the 6,000 people that were there it happened to my daughter."

Beached organisers say their thoughts are with the victim and they are doing all they can to help the police investigation. The girl's mother said: "A complete stranger raped my daughter, who was doing nothing more than going to the toilets alongside kids as young as 11. It happened 10 minutes from our home at 8pm in the evening at a supposedly safe site. How did it happen?

"I wasn't at Beached but a close friend of mine was and she says the area around the toilets was an incident waiting to happen – when it was dark people were having to use the lights on their mobiles to get about."

The friend added: "It was just so badly lit that people were having to use their mobiles to find their way around.

"There were men's toilets next to women's ones and groups of drunken men going around next to groups of kids and people pushing about, falling into one another.

"I didn't see any security patrolling that particular area, nor did anyone I spoke to.

"There were some security on an access gate near the toilets but they were giving out armbands and checking on people going in, so they were too busy to keep an eye on the loos.

"I'm nearly 40 years old and I was so worried I refused to go to the toilets unless my partner stood outside and kept an eye on it." She added that, when she returned to the festival for the Sunday show, she was surprised to find nothing had changed.

"Obviously some of the toilets were closed because they were a crime scene but half of them were open and it was still the same set-up.

"Why hadn't they separated the male and female toilets and backed them up against the sea wall where there would have at least been some light?

"I've been to loads of outdoor events and I've never seen anything like this. They made a really big thing about giving out armbands so nobody underage could buy alcohol and checking bags so no-one could smuggle booze in, so we thought it would be well policed."

In a statement to the Evening News, Beached organisers said: "Following the serious sexual assault at the Beached festival on the evening of Saturday August 16, we have been working closely with the North Yorkshire Police to help them with their investigation into the incident.

"The situation on Saturday was dealt with quickly, sympathetically and in close liaison with both our own security staff and the police, in accordance with our Major Incident Plan.

"Our thoughts are with the young woman who was assaulted, and we would like to assure her, her family and the general public that we are taking this matter very seriously and doing all we can to help the police with their inquiries."

A police spokesman said a man arrested in connection with the assault has been bailed pending further inquiries.