A 1.8-mile (2.9km) tunnel is to be dug at the A303 past Stonehenge as part of a £2bn plan to make the A303 to the South West a dual carriageway, the Government said today.

A previous plan to build a tunnel on the bottleneck route past the historic site was dropped seven years ago because of the cost.

Chancellor George Osborne said the plan would "transform" the A303 and "boost productivity" in the South West.

And Deputy Prime Minister Nick Clegg, who was visiting the area this morning, said the plan would get the funds it needs.

English Heritage, which runs the Stonehenge site, has previously described the road as "highly detrimental" to the ancient monument. The tunnel is also supported by the National Trust.

Since the tunnel plan was dropped, local councils have continued to lobby for it and the widening of the A303 and John Cridland, the boss of the CBI, has backed the idea of a tunnel.

But a group that advises World Heritage body Unesco has warned a tunnel could have an "adverse impact" on the Stonehenge landscape.

The announcement is part of the government's infrastructure plan ahead of the Autumn Statement on Wednesday with 80 new English road schemes announced in a £15 billion package

But Labour accused Prime Minister David Cameron of having "a record on infrastructure that is one of all talk and no delivery" while the RAC Foundation warned that the road network would have to cope with an expected seven million more drivers within 20 years.