New laws that allow police to search people for knives, even if they have no grounds to suspect weapons are being carried, may cause hostility among youths, the Children's Commissioner for England said on Saturday.

Sir Al Aynsley-Green said more research into the effects of increased police powers to search for knives using hand-held and walk-through metal detectors was needed.

"There's a balance here. On the one hand for young people to feel safer by having the presence of the police - but on the other hand making sure that the new powers don't breed further antagonism by increased stopping and searching," Aynsley-Green told the BBC.

"These are very contentious issues and I certainly support the case for much more research on the effects of these policies, particularly seeing the world through the eyes of the children themselves, actually asking them and making them part of the solution rather than ever being portrayed as the problem."

Officers are using powers under Section 60 of the Public Order Act which allow them to search people for knives and guns without reasonable suspicion they may be carrying a weapon.

The move follows a spate of knife crime in London in which young people have lost their lives.

Metropolitan Police deputy commissioner Rose Fitzpatrick said officers were targeting likely perpetrators.

"The work we're doing in London in particular is working alongside communities to do robust stop-and-search operations using knife arches and search wands where intelligence tells us that there is the most likelihood that people are carrying knives and weapons," she told the BBC.

"That is not aimed at victimising young people; it's aimed at keeping them safe."

Camilla Batman-Ghelidja, founder of Kids' Company, a London-based children's charity, said stop and search was necessary due to an escalation in knife crime, but blamed adults for failing to create "structures" that protect children.

"Children are feeling really unsafe. What's the point in just searching the children and not solving the core problems?" she told the BBC.