The ancient landscape of Stonehenge could be transformed by putting a major road into a tunnel past the stones, heritage groups have said ahead of an expected announcement from the government.

English Heritage and the National Trust said they were hopeful the government would announce plans to improve the A303 at Stonehenge - a notorious bottleneck that 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 area 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 tunnel with an entrance and exit below the ridges of hills either side of Stonehenge. These would have less impact than those of the 1.3 mile tunnel and would be further away from ancient burial sites or barrows which dot the landscape.

They have also suggested two 1.8 mile 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 tunnel which would remove the A303 from the World Heritage Site entirely, but recognise they have to be pragmatic.

Putting the road into one of the suggested tunnels 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.