The Metropolitan police commissioner, Cressida Dick, has said her force has turned the tide against rising violent crime in London.

She claimed there had been large reductions in the stabbings of young people aged under 25 compared with last year and said that in order to cement the improvements, officers who had been moved across from traffic duty to tackle violent crime would not be going back.

Dick told LBC radio on Tuesday: “I think we are beginning to see the tide turning in that we are putting more officers on the streets, we’re doing more stop and search, we’re seizing more knives, we’re seizing more firearms, we’re seizing more offensive weapons, we’re arresting more people for knife and gun crime.

“And we’re beginning to see, after three years of knife crime increasing, gun crime increasing, they’re now not just levelling off but beginning to come down.”

“I think that is through greater enforcement, fantastic work by my officers. That will begin to suppress and turn the tide.”

The commissioner said in November that violent crime had plateaued, which was followed by a spate of killings. On Tuesday Dick said: “I am now saying it is beginning to come down. In terms of knife crime under 25 … there is a definite downturn … knife crime itself is stabilising and beginning to come down.”

The Met released new figures on Tuesday morning backing up the commissioner’s claims.

Moving 122 traffic officers across to join the violent crime taskforce had paid off, the Met said: “The [traffic] officers joined the taskforce from September 2018, enabling the team to have a greater presence in areas with higher levels of violent crime as well as allowing more intelligence-led, targeted stop and search and the use of covert tactics.

“Since their attachment in September, they have contributed to a 31% (176) reduction in victims of knife crime with injury [under 25s] compared to September, October and November the previous year. This is part of a 12-month trend which has seen an overall 13% decrease”, which translates to 287 fewer victims.

The Met area, covering virtually all of London, had a large number of homicides in February and March, prompting the setting up of the violent crime taskforce and much greater resources being put in to tackle gun and knife crime.

The homicide rate for 2018 will be above the 123 who died in the capital last year, standing currently at 127 with three weeks of the calendar year to go.

The London mayor, Sadiq Khan, has said it could take a decade to tackle the long-term causes of violent crime. Dick said: “To stop five-, six-, seven-, eight-, nine-, 10-, 11-year-olds being dragged into criminal gangs and becoming gangsters themselves is a big, big project. It may take a long time.

“We’ve got about 180 gangs in London. They’re quite entrenched, many of them, and they’re busy bringing children in, so you have to take a long-term approach.”

The London mayor has set up a violence reduction unit to tackle the long term causes. It is unclear why violence increased, though a multiplicity of factors are suspected, including victims being involved in drugs, gangs, the effects of austerity on police numbers and reductions in youth services because of funding cuts.