Britain is struggling to get to grips with a surge of fatal knife attacks, which analysts say reflects a growing sense of insecurity on the country's streets.
While some say young people are increasingly carrying knives as a fashion item, others say it is simply because they are scared of being attacked and so make sure they are armed.
On Friday police confirmed the death of an 18-year-old in south London, the 21st teenager to die of violence in the British capital this year, amid wider concerns about anti-social behaviour among young people on the streets.
That came after nine people were killed across the country the previous week, including six in only 24 hours.
"We have seen the emergence of a worrying trend in relation to knife crime," said Scotland Yard's Deputy Assistant Commissioner Alf Hitchcock.
"We see both an intensification in the severity of offending, and a worrying change in the age profile of offenders and victims, which has decreased from mid- to late-teens to early 20s down to early to mid-teens," he added.
Analysts say young people appear to be increasingly worried about their own safety, although Home Office statistics released Thursday showed a nine percent fall in overall crime in England and Wales in the year to March 2008.
"They fear they're going to be attacked themselves," said Professor Gloria Laycock, from the Jill Dando Institute of Crime Science, named after a well-known BBC television presenter who was shot dead on her doorstep in 1999.
"I don't think it's got anything to do with some fundamental social cause like the economy, or poor parenting or anything like that, because it's happened too quickly," she added.
According to a 2006 study compiled for the Home Office, 85 percent of young people who had carried a knife said they did so to protect themselves, while 42 percent of young victims of assault went on to commit an attack themselves.
The most recent crime statistics showed there were 22,151 recorded offences involving knives last year. The highest number -- 7,409 -- was in London.
"They feel they need to have a weapon for their own protection. I think that's really the problem," said Professor Douglas Sharp, head of the Centre for Criminal Justice Policy and Research at Birmingham City University.
"Young people think that life in their particular locality is so dangerous, that there's so much threat around, that when they get into confrontations they expect to be subject to some violence," he added.
But Sharp, a former senior police officer himself, said: "Most of this violence going on is not related to other criminality, is not related to fights over drug territory or anything like that.
"It's to do with fairly mundane disagreements that just get out of hand very quickly."
Another new trend is that recent killings have taken place in public places in busy city centres, outside bars and clubs, as opposed to previously where attacks were more usually the result of domestic disputes.
"This is relatively new. Certainly in the scale we are seeing this at the moment," said Laycock.
"I think it's because it's become a kind of fashion thing. Young people have got this into their head that it's more trendy to have a knife and so they're doing that," she added.
"It has to do with their image, rather than anything more fundamental than that."
This theory would seem to be backed up by media reports, which have included photos taken from social networking sites showing young people proudly wielding knives and even machetes.
But not everyone is convinced that carrying knives is simply to be trendy.
"I don't agree that it's a fashion," said Roger Grimshaw, of the Centre for Crime and Justice Studies at King's College, London.
Research showed that young people are "more likely to have been victimised and to fear being attacked. So it's... not a trend. If they feel threatened, they try to reduce the fear by becoming threatening themselves."