Plans to dig a 1.8-mile road tunnel near Stonehenge have been given the go-ahead by Transport Secretary Chris Grayling.

Experts warned that the project would compromise the "unutterably precious" archaeology of the Stonehenge World Heritage Site.

But government heritage agency Historic England, and the National Trust and English Heritage who manage the stone circle and its surrounding landscape, welcomed the announcement.

The A303 is often gridlocked near the landmark, causing frustration for holidaymakers heading to and from the South West and disrupting visits to the site.

This year's summer holiday getaway once again produced severe delays with an hour added to the nearly three-hour trip from west London to Exeter, according to the AA.

The road is to be put into a dual carriageway tunnel with a £1.6 billion upgrade by Highways England.

Mr Grayling said: "This Government is taking the big decisions for Britain's future and this major investment in the South West will provide a huge boost for the region.

"Quicker journey times, reduced congestion and cleaner air will benefit people locally and unlock growth in the tourism industry."

The tunnel will closely follow the existing A303 route but will be a further 50 metres from the monument.

Department for Transport officials claim it will avoid important archaeological sites and will not intrude the view of the setting sun from Stonehenge during the winter solstice.

Thousands of individuals and organisations responded to a public consultation on the plans earlier this year.

Highways England chief executive Jim O'Sullivan said the A303 has suffered from congestion for many years and the scheme will "enhance, protect and restore tranquillity" to Stonehenge.

David Bullock, who is managing the project for the organisation, told the Press Association: "We're looking at a route that provides a sympathetic path through the archaeology and landscape. We're doing lots and lots of investigating."

But opponents are concerned the plan, with a tunnel past the stones that would emerge within the World Heritage Site and a bypass to the north nearby Winterbourne Stoke, would damage the wider archaeology and environment.

Time Team presenter Tony Robinson has previously described the scheme as "old-fashioned" because it "assumes what needs to be protected is that little clump of stones".

He said the stone circle was invaluable, but over the past 20 to 30 years, experts had begun to appreciate that the area around it was a complex network of henges, pathways, barrows and track-ways.

Professor David Jacques from the University of Buckingham warned that a report Highways England had commissioned on the geology underneath Stonehenge showed chalk dug up for the tunnel could damage the landscape and radon gas had been detected.

He also said the eastern end of the tunnel would threaten the archaeology of the oldest settlement in the landscape.

"The Stonehenge landscape is unutterably precious and you tamper with it at your peril.

"There should be perpetual inquiry here and the Government, National Trust and English Heritage either value that or they don't.

"The tunnel scheme will compromise the archaeology," he said, adding politicians should "stop digging themselves into an even deeper disaster".

The Stonehenge Alliance, which is supported by environmental and heritage organisations, said the plans would cause "severe and permanent damage" to the archaeological landscape of the World Heritage Site, in direct conflict with international advice to the Government.

The alliance's Kate Fielden said: "We are shocked at Highways England's indifference to Unesco's advice.

"The project needs a complete re-think, not a minor tweak which still threatens major harm to this iconic landscape.

"The potential risk of loss of Stonehenge's World Heritage Status casts shame upon our country and those responsible for caring for our heritage."

In March the International Council on Monuments and Sites (Icomos) UK, which advises United Nations cultural body Unesco, said it "firmly objected" to the proposals.

Important criteria had not been met, including ensuring the tunnel was long enough that its entrances did not harm the World Heritage Site and adequately considering options for constructing a bypass outside the 10 square mile protected area, Icomos said.

Following Mr Grayling's announcement, Historic England, the National Trust and English Heritage said in a joint statement: "This is a once-in-a-generation opportunity to reunite this ancient landscape which is currently severed by a huge volume of road traffic.

"We welcome the amended route and believe it can, if designed and located with the utmost care, deliver a lasting legacy for the World Heritage Site and restore peace and tranquillity to the Stonehenge landscape."

AA president Edmund King said the lack of progress in easing traffic jams at Stonehenge had turned it into "a monument to modern age indecision".

He added: "At last, the circle of motoring gloom has become a circle of hope for drivers."