When Carol Saldinack learned her two sons were involved in a violent, unprovoked attack which left a father blind in one eye, she rang the police and reported them.

Her sons, aged 24 and 27, were jailed for two years for grievous bodily harm. And despite being ostracised from her family as a result, the 51-year-old mother-of-six has urged other parents to follow her example.

Indeed, the Metropolitan Police Commissioner Sir Ian Blair has said that it is a parent's duty to give their children tough love'.

He said: "In the same way as you should be questioning your children about drugs and excessive alcohol, you should also be clear with them that carrying a knife outside the home is likely to lead to really serious trouble and tragedy."

The Association of Chief Police Officers (ACPO) warns that current problems with young people carrying knives, and antisocial behaviour, are not just a law enforcement or criminal justice issue. A spokesman said: "We all need to be clear about what type of behaviour is acceptable, the choices that we make in how we live our lives and how, as individuals, we can all contribute to repudiating violence.

"We need a balanced approach. More and more, parents are being encouraged to be accountable for the behaviour of their children. For some parents this is extremely difficult because their children's behaviour may be particularly challenging.

"Where parents are unable to manage the behaviour of their children, particularly in relation to the carrying of weapons, informing the police might be the action they feel they must take."

He added: "The consequences for young people who carry knives and impact on the communities in which they live are currently clearly visible on an all-too-frequent basis."

But to help beat such antisocial behaviour, parents need to start saying no' to their children much earlier and more often than is currently fashionable, said Gill Hines, author of Whatever!: A Down-to-Earth Guide to Parenting Teenagers (Piatkus, £7.99).

Gill, who also runs workshops for the parents of teenagers, said: "Tough love should start a lot younger than the teens. It is not good for kids to grow up being used to getting everything they want when they want it, or to believe they have the right to anything. What we are seeing now is in part young people who believe that."

Gill points out that if a young person is keeping behaviour secret from their parents, it can act as a boundary. For example, if a teenager were taking drugs recreationally, he might limit his use if he was seeing his mother afterwards and she openly disapproved of drugs.

"Take away that disapproval and the young person will be fine about going home wrecked, or even using at home," she said.

"Perhaps parental disapproval serves as a restraint in itself until the young person develops some sense of personal restraint, which most do."

She says the same goes for weapons, and describes how, when she lived on an East London council estate, she saw a group of youths, some of whom were armed with knives, shouting and jostling each other.

"It was getting quite serious. Then a bellow came from the next block, and within seconds three mums had marched into the fray in their dressing gowns and ticked off their kids, who went off to bed like little lambs, being scolded and shoved the whole way. That's parent power!"

Gill stresses that before calling in outside agencies like the police, parents should try talking, setting boundaries, and negotiating with their children. "If that doesn't work, the bottom line is this - Is my child a risk to someone else's child?' If the answer is yes, then you owe it to the other child's parents and family to protect them.

"There has to be a line and the line to me is if your child is posing a threat - real or possible - to others."

She says tough love means different things to different people, citing how some parents will even buy heroin for their kids to stop them stealing to fund their habit, while others will buy a burglar alarm and kick them out of the house if they persist in their habit, on the basis that most addicts need to hit rock bottom before they can pull themselves together. That's tough indeed," she said.

However, child psychologist Dr Richard Woolfson stresses that there should be no distinction between tough love and ordinary parental love. He said: "The concept of tough love suggests there are two types of love - parental love, which is touchy, sensitive and caring, and then a different type of parenting love which sets firm boundaries and guidelines. That's what we mean by tough love."

"But such a distinction is completely artificial. Parenting involves both aspects of love all the time - children need to be loved, cared for and valued, but they also need to have limits established, they need to have rules and structure. The best way to raise a child is by setting limits and providing love."

As for reporting children's bad behaviour to the authorities, Woolfson points out that although a parent's prime responsibility is to their child, there are times when external agencies need to be consulted, not necessarily for punishment, but certainly for help.

He added: "Do you know what your child is doing when he or she is out? Do you know where he or she is and who they are with? Can you talk about the difficult issues as well as the easy issues with your child?

"If you can't answer these questions with a yes' then you are potentially running into difficulties."

Dr Woolfson says parents who suspect their child is carrying a weapon, taking drugs or is involved in any other sort of challenging behaviour', should ask them about it, but in such a way that leaves room for discussion.

"Ask, rather than accuse," he advised. "The key aspect is good communication right from the start, and for you and your child to be able to talk about issues that are sometimes controversial, so that issues like drugs, drinking and antisocial behaviour are just part of the normal dialogue between parent and child."