PLAN for a £1.4bn tunnel past Stonehenge could reconnect the "extraordinary" ancient landscape which is severed by a busy road, heritage groups have said.

But the proposals for where the road would emerge west of the prehistoric stone circle need "significant improvement" as it is close to an important group of Neolithic and early Bronze Age ceremonial and funeral monuments, they warned.

Highways England is holding a public consultation on its plans for putting the A303 into a 1.8-mile (2.9km) dual carriageway tunnel where it passes the stones to cut congestion and improve the surroundings.

English Heritage and the National Trust, who manage the area, and government heritage body Historic England, said the plans would remove the majority of the existing damaging road and its traffic, which thunders past the stone circle.

It would reconnect the wider World Heritage Site, two-thirds of which lies on the other side of the road from the stone circle and which is filled with prehistoric henges, pathways and barrows, allowing people to understand and explore it better.

And plans for the eastern entrance to the tunnel would allow the reinstatement of the line of the Stonehenge Avenue, an ancient processional route to the stones, which is currently severed by the A303, the organisations said.

But they raised concerns about the western entrance of the tunnel, due to its proximity to, and impact on, the Normanton Down Barrow group, one of the key monuments for which the area is designated a World Heritage Site.

The problems could be resolved with careful and sensitive revision of the position and design of the western end of the tunnel, they said.

Kate Mavor, chief executive of English Heritage, said grassing over the A344 where it used to join the A303 and moving the visitor facilities had already shown a benefit.

"The proposed tunnel could complete that transformation and finally do justice to our greatest prehistoric monument, dramatically improving its setting and reconnecting it with the wider landscape," he said.

Helen Ghosh, director-general of the National Trust, said: "We are encouraged by the proposals put forward by Highways England for consultation but it is very clear that there's still more to do.

"The current A303 with its busy, noisy traffic ruins the setting of many prehistoric monuments in this world-renowned place. It makes it hard for people to explore a large part of the wider prehistoric landscape.

"A well located and designed tunnel would reunite the landscape, giving everyone better access and enriching their experience, as well as enabling nature to flourish."

Duncan Wilson, chief executive of Historic England, said: "The proposals could offer enormous gains, by reuniting this extraordinary landscape.

"While the design and position of the western portal needs improvement, we welcome Highways England's willingness to listen to this."

Time Team presenter Tony Robinson has joined with campaigners against the scheme, warning the proposals are "old fashioned" as they only focus on the stone circle and suggesting a longer tunnel is needed to protect the landscape.

A Highways England spokesman said: "We are working closely with key organisations within the World Heritage site, and we will continue to find the best solution possible to improve journeys for drivers while also protecting Stonehenge.

"The consultation on plans to relieve congestion on the A303 is currently ongoing and feedback we receive from everyone is really important in helping us to refine our proposed option."