Upgrading 15 miles of the A303 would cost nearly �340m

Mounting construction costs may force the government to delay the upgrading of a route through the Blackdown Hills.

The Devon and Cornwall Business Council say dualling the A303 through the hills would dramatically improve one of the main routes into the South West.

A spokesman for the transport secretary said no comment could be made yet. A decision is expected next month.

It isn't for us to prove why they shouldn't damage the landscape Jim Woolacombe, Campaign to Protect Rural England

Upgrading the 15-mile route through the Blackdown Hills, an Area of Outstanding Natural Beauty, would cost nearly �340m.

But despite this, business leaders say they prefer the plans for the A303 to an alternative plan of dualling the A358 to the M5.

But now it is feared Transport Secretary Alistair Darling may delay either project for 10 years because of feared soaring costs.

Tim Jones of the Devon and Cornwall Business Council said: "We need a firm commitment on this, we need the money ring-fenced and we need to know it's going to happen.

"A lot of businesses' decision depend on this piece of investment.

"We need to grow the regeneration of Devon and Cornwall. The Objective One programme in Cornwall particularly relies on infrastructure.

"All these things are crucially relying on this piece of investment."

Environmental groups say the plan would cause serious damage to the area's landscape and wildlife.

Jim Woolacombe of the Campaign to Protect Rural England said: "We take the view that if people want to damage the landscape they must establish their case. It isn't for us to prove why they shouldn't damage the landscape."

Members of the South West Regional Assembly agreed on the A303 in April.

However, the government's wildlife conservation agency English Nature has said it believes the A358 is still the best option.