Prime Minister Gordon Brown has vowed to fight the growing problem of teenage knife crime.

Mr Brown told police and legal chiefs on Thursday morning that anyone aged over 16 who is found carrying a knife should be prosecuted.

Under current police guidance in England and Wales, adults caught with a knife are to be prosecuted, while under-18s are to receive just a caution if it is their first offence.

"Every young person who carries a knife should be prosecuted by the courts," Mr Brown said.

"What we need to do is to make sure that if a young person is carrying a knife there is a presumption that they will end up in court and there is a presumption that they will be prosecuted.

"Even for children under 16 carrying knives we will take the toughest of actions. We want people to understand, particularly parents, that when children and young people are carrying knives they are putting children and young people at risk and the more people realise that it is unacceptable and it is wrong to carry a knife, the safer our communities will be."

Gordon Brown: "What we need to do is to make sure that if a young person is carrying a knife there is a presumption that they will end up in court and there is a presumption that they will be prosecuted."

But Professor Rod Morgan, former chairman of the youth justice board, criticised Mr Brown's plans.

"I am afraid this is an example of gesture politics reflecting the weakness rather than the strength of both the prime minister and the government," he told BBC News.

"There is no real good sense in suggesting that the guideline be changed. Isn't it odd that last week we had an announcement that four police forces are going in the future to do something called 'commonsense' policing ... that the police were going to exercise their discretion more sensibly as to how events should be dealt with locally, and now we have a suggestion that we have a presumption.

"The police have all the powers that they need to deal with what is a problem in some areas but they need to be given discretion to respond to events as they find them."

Mr Brown's latest proposals come in the wake of increasing public concern about teenage knife crime, especially in London.

Metropolitan Police figures show the number of 11 to 18-year-olds attacked with knives between April and July 2006 rose by 4.5 per cent compared with the same period in 2005.

In 2007, 27 teenagers in London were killed in knife crimes, up from 17 in 2006 and 15 in 2005.

Sixteen teenagers have already been stabbed to death in the English capital this year.