The Metropolitan police are to step up their use of targeted stop-and-search operations in high knife-crime areas of London due to a recent rise in stabbings in the capital.

The Met commissioner, Sir Bernard Hogan-Howe, said that although knife crime in London had dropped by 30% overall, with 3,645 fewer victims over recent years, there had been a 21% rise in the last 12 months – or 286 more stabbing victims aged under 25.

The fall in knife crime over the past three years has coincided with a massive scaling back of the use of stop and search by the police as a result of a campaign led by the home secretary, Theresa May, who has argued that they are a waste of police time, unfair to young black men and undermine trust in the police.

In London the use of stop and search has fallen by 40%, but the use of a more intelligence-led, targeted approach has resulted in 2,000 more arrests.

“Over the last three years we have listened to feedback from the public about too much ineffective stop and search. We have worked to make it more targeted and have seen a broad reduction in violence, shootings and stabbings,” said Hogan-Howe in a statement issued on Monday.

“But over the last three months there has been a rise in stabbings and that has caused us to review our position on stop and search. We were doing too much; repeatedly stopping people who have done nothing wrong can’t be right. But if we are getting to the stage where people think they can carry knives with impunity, that can’t be good for anyone.”

He said stop and search was a reasonable tactic when used in the right way. “We don’t want to see a return to a million stop and searches, but there is an argument for more use of stop and search focused on high knife crime areas and targeting gangs,” he said. “Our 1,200 Trident gang crime officers have a big part to play in this.

“If we know people are violent and carry knives, then we have the power to prevent them hurting people and we should stop and search them every day,” he said.

The London mayor, Boris Johnson, said he believed action was needed to ensure that the “blip” in the rise in stabbings did not become a trend in the capital. Johnson and Hogan-Howe are also pressing ministers to enact new legislation introducing a mandatory six-month prison sentence for those convicted of a second offence of being caught with a knife. They say although the measure has reached the statute book, the Liberal Democrats blocked its implementation under the coalition government.

May agreed that stop and search should only be used in a targeted way that improved the ratio of stops to arrests. She said: “I have been clear that stop and search is an important police power, but, as with all sensitive powers, it must be properly targeted, based on reasonable grounds and accountable to citizens and communities.

“I have already introduced the ‘best use of stop and search scheme’ to bring greater accountability to the use of these powers and revised the police and criminal evidence code to make it clear what constitute reasonable grounds.

“But, as I have always said, if the use of these powers does not become more targeted, and stop-to-arrests ratios do not improve, then I will bring in primary legislation to make it happen,” she said.