London Mayor Sadiq Khan has announced £13 million in new funding to tackle serious youth violence in the capital, partly funded by the sale of Boris Johnson’s ill-fated water cannon.

The crowd control machines, bought and refurbished for more than £320,000, have been sold as scrap metal for just £11,025. Khan said “it beggars belief” that his predecessor had spent “so much money” on the cannons, calling it a “vanity project where taxper money was wasted”.

Khan said he would “use the proceeds of the sale to invest in young people”, following a spate of youth violence in the capital which saw four people stabbed  in Enfield at the weekend. 

The fate of the water cannon, announced on Monday, prompted an outpouring of scorn directed at Johnson. Labour’s David Lammy said in a tweet: “Not sure what’s devalued more, the value of Boris’s water canons or his own career.”

The water cannon saga has been a long-running embarrassment for Johnson who purchased them from Germany in 2014.

A year later then-Home Secretary Theresa May torpedoed the scheme, saying she would not give permission for police to use the devices as part of riot control techniques, citing safety fears as a major factor.

Khan announced the new funding at Spotlight in Poplar, a youth centre which provides music, dance, art and theatre programmes, and is one of 72 projects due to receive the funding.

He said: “Young people, rather than having constructive things to do, are joining criminal gangs and think it’s okay to pick up knives.”

Asked about the spate of violent attacks across the capital this weekend, Khan said: “My message to Londoners, particular in Enfield, is to help the police carry out their investigations.

“I’ve met too many victims of violent crime, too many bereaved families, it’s really important that we help the police when they carry out investigations.”

London has seen a 16 percent rise in stabbings this year and there were 1,299 up to the end of April, according to official statistics from the Met Police.

While visiting the Spotlight centre, Khan watched performances from young Londoners, some of whom are aspiring singers and rappers. Isaac Abuwa, from south east London, said the visit from the Mayor was important for people who attend the centre.

The 16-year-old, who raps under the stage name XI, said: “You see a lot of stabbings now, a lot of gangs, a lot of drug violence.

“My music is trying to help the young people, trying to put them out of a place, a form of escapism.

“He said my music was good and I really appreciated that, coming from the Mayor himself, I really liked that.”

Aaron Williams, a creative youth worker at Spotlight, said: “To have the Mayor here was amazing and I think, more than anything, him giving feedback to the young people is going to give them that extra bit of encouragement to go forward in their careers.

“I’m finding, through my youth work, that a lot of the young people that are perpetrators of these violent acts don’t have much to do.

“They’re stuck at home, bored, or out on the street, bored, and they’re just getting up to mischief.

“More than anything we want to give them something to do that they can look at and takeaway and be proud of and create something from their own imagination.”