The government has been accused of “sitting on its hands” after promising emergency funding for police to tackle violence.
The Home Office said £51m was being made available for more patrols, weapon sweeps and officer overtime ahead of the Easter weekend.
Last Easter saw a spate of brutal street murders in London, with 17-year-old Tanesha Melbourne-Blake murdered in a drive-by shooting and a 16-year-old boy shot in the face on the same night.
But the extra funding was dismissed as “loose change” by critics, who pointed out Philip Hammond had announced £100m last month.
The chancellor had enraged forces by initially telling them to use existing budgets to tackle knife crime and divert resources from “lower priority areas of policing”.
“If your house is on fire, you stop painting it and you go and get a bucket and start pouring water on the fire,” Mr Hammond said in March.
He performed a U-turn days later, telling the House of Commons he and Theresa May had “decided, exceptionally, to make available immediately to police forces in England an additional £100m over the course of the next year”.
But the funding falls far short of the £200m to £300m requested by police chiefs, and is only going to 18 of the 43 forces in England and Wales – including the Metropolitan Police, Greater Manchester, West Midlands and Merseyside.
The Home Office said that a third of the £100m has been ring-fenced for violence reduction units, which include councils and health agencies as well as police.
Of the remaining £65m, £51m was made available on Wednesday and the last £14m will be allocated “in due course” to forces seeing increasing violence.
National Police Chiefs’ Council chair Martin Hewitt said the heads of each force would decide how to use the extra money.
“This will help forces to carry out activity that we know works, such as increasing the number of officers available to carry out targeted patrols in crime hotspots and increase our use of stop and search,” he added.
“Police tactics alone will not prevent violence, however, and any solutions must involve government, education, health, social services and communities themselves.”
The government’s first-ever Serious Violence Strategy, launched last year, pointed to drug dealing and social media as drivers of violence.
But youth workers say austerity and exploitation have created a “lost generation” of children, and left police without the resources to respond.
Sadiq Khan accused the government of “breaking its promise immediately to give the Met and other police forces across the country £100m of emergency funding to tackle violent crime in the days and weeks ahead – just when it is most desperately needed”.
“Ministers have sat on their hands for more than a month and have not even allocated the full amount of funding that they promised,” the Labour mayor of London added.
“This is symptomatic of a government that has cut police and preventive services to the bone and buried its head in the sand over the impact of austerity. It is time for proper action, and that must mean fully reversing the damaging cuts to the Met and youth services in London since 2010.”
A National Audit Office report found that police funding fell by 19 per cent in real terms between 2010-11 and 2018-19.
The number of police officers in England and Wales plummeted by 20,000 in the period, but rose modestly after an annual funding boost from Sajid Javid.
The home secretary insisted police had the government’s full support.
“Knife crime destroys lives and as home secretary I’m determined to do everything in my power to stamp it out,” Mr Javid added.
“This funding will help the police forces worst affected by violent crime to up their response, including by increasing the number of officers out on the streets over the Easter weekend.”
The Police Federation, which represents rank-and-file officers, dismissed the funding as “pocket money”.
Chair John Apter said: “It has taken the government more than a month to finally make this cash available to chief constables.
“In the meantime, our communities continue to be blighted by the violent crime epidemic and our members continue to do their very best to tackle it with the limited resources available to them.”
Mr Apter called for the police funding formula to be changed to ensure police are adequately resourced, adding: “Any additional funding is welcome – but this is loose change when you consider the scale of the issues facing policing, and the communities we serve.”
Mark Burns-Williamson, head of the Association of Police and Crime Commissioners, said the money allocated to violence reduction units would help prevent crime as part of the “public health model” used successfully in Scotland.
“This funding should be distributed at the earliest opportunity,” he added.
There were 285 homicides caused by a knife or sharp instrument in England and Wales in 2017-18 – the highest number since records started in 1946.
In the year to September, police recorded around 1.5 million “violence against the person” offences – a jump of nearly a fifth on the previous 12 months.