Mr Moore said he was deeply concerned after the clash, which came as he joined officers on a routine patrol on a Friday night.

The chief, who himself has a 15-year-old son, is also worried by the growing trend of teens using sites like Facebook and Twitter to bully and inflame feuds between youngsters.

His unease has grown because the mob of between 30 and 40 13 to 15-year-olds had met after a girl had used a social networking site to boast that she was going to stab another girl.

He said: “Several said a certain girl had been on a social networking site and had threatened to stab another girl. Everyone had turned up to see what was going to happen, which amazed me. When I asked why they were not at home everyone said they were staying at a sleepover.

“I kept thinking: ‘Where are the parents in this? Do their parents know where these kids are?’ They’ve got themselves on a social networking site and turned up to possibly watch a stabbing and I just thought to myself ‘this can’t be right’.”

Over the course of 90 minutes up to seven officers were involved in keeping the peace. One 14-year-old boy was arrested for being drunk and disorderly.

Mr Moore said: “I’m not saying this to accuse, I want to stimulate a debate. My son is 15, so I’m living this. This has made me think about my own son. I would be horrified if I thought my son was putting himself near something as serious as that.

“I will be tasting my own medicine. I always want to know where he is when he goes out, while giving him a reasonable independence.

“Parents have a significant part to play. Do they know where they are?

What they are doing?

Are they safe? Where are they in the virtual world?

Trusting kids is important but supervising them is essential.”

He said the challenges posed to modern parents are a unique consequence of the rise of social networking sites in recent years.

“I absolutely think there’s something unique about this,” he said. “In the past you could have a phone conversation with one friend and there was no permanent record for others to comment upon.

“Here we have a semi-permanent record, everyone can add to it.

Things can be whipped up. It’s a place where the normal culture of respect and dignity can be eroded. People can get so wound up. You get lots of tit-for-tat comments.”

“I’ve spoken to parents and they all agree it’s a really difficult thing.

One woman told me her 15-year-old son came home on Friday and told her there was a great big fight and she was really worried.”