A spokeswoman for the National Police Chiefs' Council said that the forces’ decision to use cameras was "an operational matter", adding that "all forces have individual responsibility for their use of speed cameras".
Edmund King, president of the AA added: "Many of the empty yellow cases are due to cuts in road safety grants and the fact that digital cameras, although more effective, are very expensive.
"It is also reflective of the fact that proceeds from cameras are no longer allowed to be ring-fenced to be reinvested into yet more cameras as now all the money goes to the Treasury."
However he warned that drivers should not assume cameras are not working.
He said "Drivers who play Russian roulette with fixed-site speed cameras are playing a dangerous game. Our advice is stick to the limits rather than gambling on the yellow boxes."
Claire Armstrong, co-founder of lobby group Safe Speed said: "Forces are conning the public into thinking cameras are there for road safety because, if they really thought that, every single one of them would be on.
"They are a flawed road safety policy and the only way to truly improve that is with more traffic police officers on the roads."
She added: “I am glad there are only 52 per cent working - and we'd actually like to see less."
