The Prime Minister has promised new stop-and-search powers to crack down on knife crime in London if he is re-elected.

Boris Johnson said new court orders would allow police to stop criminals who are known to carry weapons.

The Prime Minister told the Evening Standard that anyone arrested on suspicion of carrying a knife would be charged within 24 hours, and appear in court within a week.

He also promised a new Serious Violence Reduction Order, which would be applied by courts to anyone receiving a community order, suspended sentence or jail time for knife crime.

The order would allow police to arrest known offenders without suspicion for the duration of their sentence.

Mr Johnson would also spend an extra £35 million on violence reduction units in crime hotspots – including London – next year. It is not yet clear how much funding would come to the capital.

Speaking to the Standard, the Prime Minister said he would use his experience as Mayor to “come down hard on knife crime in London”.

He said: “I know the importance of successfully fighting crime in this city and that’s exactly what a Conservative government will continue to do.”

But opposition politicians have questioned the policy and attacked Mr Johnson’s record on crime during his time as Mayor.

Liberal Democrat assembly member Caroline Pidgeon accused the Prime Minister of “resorting once again to gimmick announcements”.

She said: “The last few years of Boris Johnson’s time as Mayor of London saw fatal stabbings increasing across the city.

“Boris Johnson should be totally ashamed of his record, but instead he is trying to make political capital out of the issue.”

She added: “The police already have the opportunity to stop and search anyone they have the intelligence to believe might possibly be carrying a knife.

“The police should not hesitate to properly use that power, but simply resorting to blanket use of stop and search leads to tension and division in local communities, with the trust between young people and the police often totally lost, with huge consequences for the future.

“Far from learning from his past mistakes Boris Johnson is just adopting simplistic policies to complex issues.”

A spokesperson for London Labour said: “It is difficult to take any of this seriously given it was a Tory government that cut police numbers in the first place.

“Their austerity has contributed to violent crime rising since 2014, as well as bringing our courts and justice system to its knees.

“For all the bluster, not a single one of the new officers the Prime Minister keeps mentioning have been recruited.”

Mr Johnson promised 20,000 more police across the country, with almost 1,500 of those set to join the Met next year.

The new officers have not yet been funded – and the Metropolitan Police Federation has said more recruits will be needed to tackle violent crime.

But Conservative London mayoral candidate Shaun Bailey welcomed the Prime Minister’s plans today, and said serious violence was “getting harder to escape”.

He said: “Gangs are recruiting younger kids to run their product and that’s forcing our young people to arm themselves in a misguided effort to protect themselves.

“It has to stop. At the end of the day, criminals fear one thing: being caught.

“The new measures being put forward by the Prime Minister send a strong signal – commit knife crime and you will be caught and prosecuted.”