The poverty and hopelessness that fuel violence have worsened during the coronavirus lockdown and offending will increase unless the government finds more money to thwart a crime rise, Sadiq Khan has said. The mayor of London has demanded the prime minister spearhead efforts to stop a rise in offending that police around the country have raised fears about as relaxed lockdown restrictions allow more people back on to the streets. Khan said there was a “proven link” between rising poverty, increasing deprivation, increasing mental health problems and rises in serious violence. In a letter to Boris Johnson seen by the Guardian, he says deepening poverty caused by the economic damage from the virus may result in rises in crime: “We should be under no illusion that the underlying causes of violence have gone away,” he wrote. “I am deeply concerned that many could be made far worse by the current crisis and its economic consequences, and that with our police service more stretched than ever, violence could resurface as soon as lockdown is eased.” Khan said young people had been hard hit, with their mental health suffering after they lost diversionary activities and the ability to see their friends and youth workers during the lockdown. “We know that the most vulnerable young people have struggled to access the same level or quality of interaction with education and youth services that they have previously relied on. I have also seen data which shows that these disproportionalities are even wider for the most deprived households,” he added. “This is deeply concerning given the proven link between serious violence and deprivation, poor mental health and poverty.” Figures from the Metropolitan police, which covers London, show that since 12 March there have been huge falls in crime compared with the same time last year. Total offences in the biggest police force area in the UK are down 32%, burglary has fallen 38%, robbery is down by 48%, theft is 56% down and violence with injury has fallen by 25%. Khan said Johnson should invest more money in things for the young to do, especially if the lockdown was eased more as the long school summer holidays started. He wrote: “It is therefore essential that the government gives the strongest consideration to young people in its lockdown exit strategy. Otherwise, there is the serious risk of a return to previous levels of violence in London and in other major cities across the UK.”