An upgraded route would help traffic flow to Devon and Cornwall

Proposals to dual the route, one of the country's worst bottlenecks, are being considered by the government.

It had been suggested that the sale and expansion of Exeter Airport, which is alongside the route, would favour it over the alternative of dualling the A358 to the M5.

But that has been dismissed by Taunton MP Adrian Flook.

He is in favour of dualling the A358 instead, and says people in Dorset and Somerset would be more interested in using Bristol Airport than Exeter.

He also says the A30/A303 expansion through the Blackdown Hills Area of Outstanding Natural Beauty (AONB) may help some parts of Devon, but is incredibly environmentally damaging.

He said: "The government as far as I am aware are not proposing Exeter airport for expansion and if they are proposing that it is many years away and well beyond the remit of anyone to look at planning requirements regarding the A303 against the A358."

The A30/A303 dualling scheme, which would cost �337.9m, is shorter than dualling the A358 and is favoured by Devon County Council and the South West Regional Assembly.

The county council has calculated that vehicles travelling via the A358 and M5 would cover an extra 32.8m miles a year.

But Friends of the Earth say that an increase in carbon dioxide emissions is a price worth paying to protect the ancient landscape of the Blackdown Hills.

Devon County Council decided last week to sell at least three quarters of its shares in Exeter airport because it could not raise the funds needed to invest in a planned new terminal building.

The Devon and Cornwall Business Council says if the new buyer goes ahead with those plans, the government could favour dualling the A30 and A303.

However, Department for Transport guidelines include a "strong presumption" against routes that would damage such areas.