The A303 can be a nightmare for tourists in the holiday season

The Highways Agency report deals with two options: dualling the A358, which links the M5 with the A303, or dualling the A303 through the Blackdown Hills, an Area of Outstanding Natural Beauty.

It does not reach any firm conclusions about the Blackdown Hills proposal, although it does not find many advantages to dualling the road.

It says widening the alternative A358 route between Ilminster and Taunton would be more cost effective.

The combination of dual and single carriageways on the A303 from Honiton in Devon to the M3 causes major traffic jams in the summer as people flock westwards for their holidays.

The proposals have caused friction between business leaders in Devon and Cornwall and Somerset.

Somerset business leaders want the A358 between Ilminster and Taunton to be dualled.

They say dualling the A303 through the Blackdown Hills would mean delays for inquiries and the certainty of environmental protests.

But Devon and Cornwall business leaders, pointing to a resurgence of holiday traffic, especially to Cornwall, want the A303 to be dualled.

The government faces a tough decision, because even though there is a presumption in favour of avoiding dual carriageways through Areas of Outstanding Natural Beauty, if they divert the extra traffic onto the M5 it could cause problems there.

More holidaymakers

Transport minister David Jamieson said: "We have seen enormous increases of traffic going through the area.

"This is partly because of the renewed success of the economy in Cornwall and west Devon.

"We are also seeing more holidaymakers coming into the area throughout the year, not just the summer, and we are seeing commercial vehicles going in and out for economical purposes.

"That obviously has to be reflected in the sort of decision-making that we have."

A series of meetings, which start on Friday, will be held with local politicians to get their views, before government ministers make a final decision on what action to take.