A teenage girl was passed around a gang of youths in a drug-fuelled orgy on Primrose Hill as families looked on.

It is believed the girl – thought to be 14 or 15 years old – was being “initiated” into a gang and police fear the encounter was not “wholly consensual”.

The incident, near Elsworthy Road, is thought to be the latest in a string of sex “line-ups” in the park where girls are coerced into having sex with a group of boys. The incidents are often recorded on mobile phones and released on the internet.

“I can only imagine the horror that these girls have to go through knowing that their exploits will be passed around or even put online,” said a police source.

Emily, a reformed gang member whose name has been changed to protect her identity, said that line-ups are commonplace among Camden gangs.

Boys form a queue as the girl is forced to perform sex acts with them, she said.

“The girl can be intimidated because normally there is a big group of boys and she feels she has to do it or otherwise who knows what they’ll do,” said the 20-year-old, from one of the borough’s most notorious estates.

The teenage girl involved in the latest incident had been lying on the grass on Primrose Hill with a male companion when the pair were approached by a group of young men last week.

Police believe drugs were traded and smoked before the girl had sex with several of the youths at about 5pm in full view of young families.

Trish Bertram, a regular walker in the park, said: “This beautiful part of London attracts tourists and people of all ages on the weekend.

“It’s a lovely place for peace and quiet to enjoy the ambience. So it’s quite shocking that something of this nature could happen here.

“It’s quite shocking to hear that it could happen anywhere but it’s sad to hear that it has come to this sleepy part of north London.”

Police have issued a plea to dog walkers to keep a lookout for similar incidents. Anyone who spots a similar case should call 999 immediately.