A war of words erupted yesterday over long-awaited improvements to one of the most dangerous roads in Britain.

A leading environmental group labelled proposals to dual the entire length of the A66 - where 70 people have died in the last decade - as unjustifiable.

But their view was angrily dismissed by campaigners at the A66 Completion Group, who said the claim flew in the face of all the known facts about the issue.

Last autumn an independent safety study carried out on behalf of the Government recommended that full-scale dualling was the only long-term solution to the road's problems.

However Transport 2000 commissioned their own report from road safety expert Professor Richard Allsop of University College, London, and he has come to a completely different conclusion.

He believes the original consultants were over-cautious in their estimates of the likely casualty savings from small scale improvements such as speed management, traffic calming and junction work.

Such small-scale works could be implemented quickly and at much less cost _ between £1m and £3m compared with £66m for dualling.

Prof Allsop, who is also the director of the Parliamentary Advisory Council for Transport Safety, said diverting cash from elsewhere to accelerate dualling the A66 would be a "serious exacerbation of an already clear misallocation of resources."

He added: "If resources were diverted, and this was used as a precedent for similar decisions elsewhere, the consequences would be damaging top road safety policy."

Transport 2000 are now using Prof Allsop's conclusions to strengthen their own opposition to the scheme.

"Any attempt to erode the inherent character of the landscape and impose an infrastructure that is out of keeping with the surroundings will seriously detract firm this highly distinctive area," said spokesman Jane Parsler.

But the chairman of the A66 Completion Group, Michael Heseltine, said: "A vast amount of time and resources went into the safety study which looked at all the pros and cons before coming to the categorical conclusion that the only answer was complete dualling."

And a spokesman for North Yorkshire County Council said other environmental groups like the CPRE had backed the proposal and added: "In our view the need to improve the safety record goes a long way towards outweighing the environmental impact."