A motoring group yesterday described new Government guidance on speed limits for local roads as "flawed and deadly".
Transport Minister Stephen Ladyman wants local councils to review speed limits, with the possibility of some roads having lower limits.
But the Safe Speed road safety organisation said: "The new guidance is based on faulty foundations and will ultimately cause road deaths to increase."
And the AA Motoring Trust said speed limits must reflect the realistic conditions and not be imposed because of dogma.
The new guidance from the Department for Transport is designed to promote greater clarity and consistency. It covers the setting of all local speed limits on single and dual carriageway roads.
Traffic authorities have specifically been asked to review the speed limits on all of their A and B roads and implement any changes by 2011.
Mr Ladyman said: "Realistic and consistent speed limits help to keep traffic moving freely and safely. Our new guidance encourages lowering speed limits where the evidence warrants it but equally traffic authorities should consider increasing limits if it can be done safely.
"The guidance also encourages traffic authorities to set limits that reflect the road environment and characteristic, and which drivers will instinctively understand."
The guidance takes account of road safety developments, including speed limits in villages and 20mph zones.
There are no plans to change national speed limits, namely the urban 30mph speed limit on street-lit roads, the national speed limit of 60mph on single carriage-way roads, and the 70mph limit on dual carriageways and motorways.
Safe Speed founder Paul Smith said: "The DfT does not understand the process of safe driving and as such is not competent to devise road safety policy."