ONE of the south’s most famous sites could be transformed by plans to run a tunnel past it.

English Heritage and the National Trust said they were hopeful the Government would announce plans to improve the A303 at Stonehenge - a notorious bottleneck which is ''highly detrimental'' to the ancient monument - with a tunnel bored underground.

Officials had come to English Heritage, which looks after Stonehenge, and the National Trust, which owns much of the land in the wider World Heritage Site, earlier this year with three proposals for improving the A303.

The options were dual carriages further to the south or north of the stones or a 1.3 mile tunnel along the current route of the A303, a scheme previously proposed a decade ago but abandoned in 2007.

The heritage groups said the three options were unacceptable, and have drawn up alternatives which they consider would be beneficial to the World Heritage Site, two-thirds of which is inaccessible to the public because it is cut off by the A303.

They include a 1.6 mile (2.5km) tunnel, whose entrance and exits are below the ridges of hills either side of Stonehenge to have less impact and further away from ancient burial sites or barrows, which dot the landscape, than those of the 1.3 mile tunnel.

They have also suggested two 1.8 mile (2.9km) tunnels, one following the line of the road, and another veering slightly to the south of the existing A303, which they said would be even more beneficial.

The organisations admit they would most like to see a 2.8 mile (4.5km) tunnel which would remove the A303 from the World Heritage Site entirely, but recognise they have to be pragmatic about what can be done about the road.

Putting the road into one of the tunnels the groups have suggested would open up the landscape of the wider World Heritage Site, allowing people to explore it, and restore tranquility to the stones which are currently affected by road noise, they said.

The National Trust has been restoring the land from arable production to semi-natural chalk grassland, boosting species from brown hares and Adonis blue butterflies to cowslips and prickly poppies, and burying the road would also have benefits for wildlife.

Cassandra French, of the National Trust, said: ''Our starting point is the existing road is highly detrimental to the the World Heritage Site. It cuts off two-thirds of the site to the south, it affects the setting of the stones and has an impact on wildlife.

''We would love a 4.5km tunnel to be announced, to be on the table, but what we did was try to take a proactive, pragmatic approach to what might be acceptable to us. This is about what is deliverable long term.

''We want to see the longest tunnel possible but we didn't want to rule out good options that would remove substantial parts of the road.''

Phil McMahon, inspector of ancient monuments in Wiltshire for English Heritage, said: ''What this is about is the Government gets the traffic moving but we protect what's special about Stonehenge and all the other monuments.''

The announcement expected next week will be the latest in a long line of attempts to sort out the roads around Stonehenge, which have been recognised as a problem for the World Heritage Site for more than 30 years.

Last year, the A344 past the stones was closed and a new visitor centre opened 1.5 miles away from Stonehenge as part of efforts to improve the immediate setting of the site, which attracts more than a million visitors a year.