Older equipment that uses radar, which makes up more than half of the city’s 49 fixed speed cameras, is only approved for use by the Home Office for speeds over 30mph.
After police said that any 20mph speed limit would not be “routinely enforced”, fears are growing that the new rules will prove toothless.
Supporters of the council’s move to slash speed limits on 80 per cent of city streets have called for the scheme to be properly enforced, amid fears drivers will flout the new rules.
Institute of Advanced Motorists director of policy and research Neil Greig said there were now serious question marks over plans for a 20mph limit in so many streets.
He said: “Without Home Office-type approval, authorities cannot reliably use speed readings to prosecute drivers as they might be challenged.
“This does mean that Edinburgh could seek the correct approvals, although it may take some time to get them.”
A similar issue affecting breathalyser equipment only approved for use to enforce the UK drink-drive limit delayed the implementation of tighter rules for Scotland until just before Christmas.
The Lothian and Borders Safety Camera Partnership operates 34 of the affected cameras within the city manufactured by Dutch company Gatso, three of which – at Melville Drive, Corstorphine Road and Niddrie Mains Road – are on streets within the 20mph scheme.
Several more of the affected speed cameras are just outside proposed 20mph areas. Another 15 cameras using different technology are operated around the Capital, as well as five mobile units.
Scottish Conservative MSP Alex Johnstone said conflicting messages about enforcement were “only going to cause more confusion”.
He said: “This is another revelation which shows just how excessive and illogical this plan is. Speed cameras which motorists know fine well don’t work are only going to cause more confusion.
“Only roads where there is an absolute safety need – like near schools – should be subjected to 20mph limits. Otherwise, the council will end up holding the whole city up.”
Council officials have said there are no plans for expensive traffic-calming measures to back the new speed regime, with street signs the only infrastructure changes mooted.
However, in a letter to the Evening News today, transport leader Lesley Hinds said illuminated signs with radar technology that remind drivers of the speed limit could be installed.
A study conducted following 20mph pilots in Portsmouth found that speed signs alone only resulted in a 2mph reduction in average speed.
A Lothian and Borders Safety Camera Partnership spokesman said: “The partnership is discussing the implications the speed limit reduction may have with the council.
“The technical issues vary depending on the type of safety camera installed.
“The partnership will know more once the council vote takes place and we will then begin to look at the technical and practical issues in detail.”
A council spokeswoman added: “Enforcement of 20mph speed limits using cameras is being discussed with the Safety Camera Partnership.”
Tories to oppose plans
CONSERVATIVE Party councillors on the transport committee will today oppose plans to introduce 20mph speed limits on four out of every five city streets.
The measures are being voted on, with the Tory group saying it is “concerned that taking this action forward at this time . . . will lead to significant objections which will make the network proposed unsupportable”.
Transport spokeswoman councillor Joanna Mowat said the plan was uncosted, and that money should be spent on filling potholes instead.