Police are facing a “new era of austerity” with some forces potentially facing their worst ever annual budget cuts fuelled by the coronavirus crisis. The mayor of London, Sadiq Khan, has warned the funding crisis endangers the government’s pledge to recruit 20,000 extra officers to fight crime and risks leaving police “with one hand tied behind their back”. One senior police source told the Guardian that a combination of factors could leave forces across England and Wales in “dire trouble”, with looming annual cuts more severe than during the austerity era Boris Johnson vowed to leave behind. Police forces have spent extra money on protective equipment and computers during lockdown so officers can work from home, in addition to running a standard police service, with costs running into an estimated £100m from March to June. They also face potential cuts in the money they get from local authorities, with one private estimate of £250m. The government is under pressure to announce if it will provide extra funding. Police forces fear a repeat of 2019, when pay rises for officers were not funded by government and had to be paid for out of existing budgets, meaning they faced a real-terms cut. Police across England and Wales have also lost income they get from policing airports and football matches because of the pandemic. Khan, who as London mayor oversees the largest force, the Metropolitan police, warned the shortfall “could jeopardise our ability to tackle violent crime at this crucial juncture”. In a letter sent to the home secretary, Khan warned of a “new era of austerity” for police, with frontline officer numbers under threat and the danger of crime rising. He said government cuts to police funding after 2010 had “disastrous consequences for violent crime”. Khan wrote: “I have protected policing as much as is possible from these cuts – but it still leaves a £109.3m budget reduction over the next two years.” Boris Johnson’s government has promised an additional 20,000 officers to reverse cuts made by his Conservative predecessors. Since the crisis caused by the pandemic, the prime minister has pledged the multibillion-pound bill will not be paid for by a return to austerity. One force told the Guardian it expected bigger annual budget cuts than in the years of austerity. “We hope to make a case to government to give us a better settlement than we are fearing,” a senior source said. The force in question is actively considering moving uniformed officers into civilian roles and making staff redundant. That means new officers will not be fighting crime but instead be in offices and call handling centres: “We could meet the headline number of [new] officers but more are pushing pens to help with the big savings,” one source said. In his letter to the home secretary, seen by the Guardian, Khan wrote: “I am therefore asking you for urgent support to protect our police from a new era of austerity … to provide funding to make up for lost expenditure to stop the inevitable knock-on impact on police funding.” The London mayor, criticised by opponents for being quick to blame the government, wrote: “If we don’t have certainty from the government over funding now, I am concerned that we will not be able to afford the early recruitment of 600 new officers as planned. We would also need to consider recruitment freezes in staff posts across the Met, which would risk affecting core services such as the handling of 999 calls and vital intelligence and forensics services. “I fear that failure to act quickly will not only put the government’s pledge to recruit 20,000 additional officers over the next three years at risk and damage services that help to tackle the root causes of crime, but will leave the police with one hand tied behind their back at the worst possible time.” David Jamieson, the police and crime commissioner for the West Midlands force, which is the second biggest in England and Wales, said: “There is a significant risk around future council tax income that is going to be a major issue across the public sector including police forces. “In addition Covid has so far cost West Midlands police around £11m with further costs to come and no guarantee that the Home Office will cover these costs.” There are 43 forces in England and Wales covering local areas, and each relies on local funding to different degrees. For some it is as much as half their funding, while for others it is a fifth or less. A Home Office spokesperson said the government was working with police forces on the funding they would need in the future and the extra burdens caused by the pandemic. “This year we have given policing its biggest funding boost in a decade – an increase of up to £1.1bn compared to last year – and this significant investment will help police forces meet financial pressures. We have already recruited 3,005 of the additional 20,000 police officers and have no plans to slow down as having more officers on our streets is now more important than ever,” they said.