The controversial stop and search policy, which has been criticised for unfairly targeting black youths, was today described as 'loving and kind' by the Prime Minister, Boris Johnson.
During a live Facebook public question time Mr Johnson was asked how he would tackle knife crime, which has seen 86 deaths in London this year.
Figures have also shown knife crime in England and Wales has soared to a record high, with 43,000 offences last year, while in Scotland police arrested 2,364 people last year who had knives in their possession - a hike from 1,879 cases recorded five years ago.
Condemning knife crime as a "scourge", Mr Johnson said that while he realised stop and search was "controversial", it needed to be "part of the mix" for police officers.
Reflecting on his time as London mayor, he said: "In a way it goes in waves, we had a terrible outbreak, ten or 12 years ago, young kids were dying at a rate of 30 a year in knife violence in London,
"We did all sorts of things to intervene with the kids... we sponsored mentoring schemes and youth clubs and tried to help kids get apprenticeships and good jobs.
"But we also had a very tough law and order driven approach. We had a lot of stop and search and we took about 11,000 knives off the streets and serious youth violence came way down and the murder rate was more or less reduced by 50 per cent.
"So you need to do both things. That's why we're putting another 20,000 police officers out on the streets, and changing law on stop and search to give police a bit more confidence... to give them the backing to do stop and search which is an emotionally challenging thing for a police officer to do, as well as difficult for the person being stopped and searched.
"I know it's controversial and people say certain groups get picked on by the police, black and ethnic minority groups in particular, and they'll say it's unfair. I say you do need to do it it has to be part of the mix.
"And I think the most loving and kind thing you can do to a young person who is carrying a knife and maybe endangering his life - and it's nearly always a he - and the lives of others, is to take that knife of him and that's why we're doing it."
Mr Johnson also linked crime with mental health issues adding: "The problems of youth crime and youth violence, and indeed crime of all kinds, are associated with mental health problems and I'm absolutely certain what you need to do to help tackle mental health issues, is that every aspect of the state that has a care for mental health patients of all kinds - social services, housing ,police, councils, probation services - you need wrap around care for people.
"And we need to escalate the issue and be much less afraid as a society in talking about mental health problems, talking as a society about the issues we face, that's the way we get it done and we beat it."