The number of speeding drivers escaping with warnings is rising due to police cuts.
Road safety campaigners have accused the Government of putting lives at risk by using volunteers to use speed guns in place of officers, when motorists can only be prosecuted if caught by police.
Last year, 50,000 warning letters were sent to those caught, up from just 10,000 in 2009.
Police chiefs fear motorists will be let off with prosecution as officer numbers are slashed, speed cameras are switched off and road safety spending is axed under George Osbourne’s cuts.
Police chiefs need to axe 16,000 officers as the Chancellor slashes 20% from force budgets.
This comes as town hall chiefs have given volunteers speed guns to monitor streets under schemes such as Community Speedwatch. They were issued 157 radar kits over the last three years.