A legal challenge is being launched to halt government plans for a two-mile tunnel under Stonehenge that will cut through a world heritage site.

Earlier this month the transport secretary, Grant Shapps, approved the £1.7bn project, which will include 8 miles of extended dual carriageway along the A303 in Wiltshire.

The campaign group Save Stonehenge World Heritage Site (SSWHS) has commissioned the law firm Leigh Day and barristers Victoria Hutton and David Wolfe QC to investigate the lawfulness of the decision.

Shapps has been served with notice of potential legal action and asked to respond within 10 days. Any judicial review will need to be started by 24 December.

Earlier this month the transport secretary overruled a report by five planning inspectors who recommended withholding consent. The road improvements are intended to widen traffic bottlenecks on a major route to south-west England.

Historic England and the National Trust argue that diverting the road underground will enhance the site. Druids, green campaigners and archaeologists have opposed the plans.

Shapps accepted the development will cause harm to the 4,000-year-old Unesco world heritage site but concluded it would not be substantial and would be outweighed by the public benefit.

SSWHS, a new organisation set up by supporters of the Stonehenge Alliance, has begun a fundraising campaign to pay for the legal action. In its letter to Shapps, the organisation said the proposals were in breach of Unesco’s world heritage convention.

Tom Holland, president of the Stonehenge Alliance, said: “I fully back the move to test whether Grant Shapps acted legally in approving this highly wasteful and destructive road scheme. The government has ignored advice from both Unesco and the independent panel who presided over a six-month examination.

“To have won the arguments based on reason and evidence, and then to have them overruled on a ministerial whim, shows just how broken the roads approval process is. There is still a chance to stop the bulldozers moving in and vandalising our most precious and iconic prehistoric landscape.”

Rowan Smith, a solicitor at Leigh Day, said: “Our client believes that there is a legal case to be made that the secretary of state unlawfully assessed the harm that is going to be inflicted on a 4,000-year-old and much cherished world heritage site, deciding instead that such destruction is a price worth paying for the economic benefits and faster road travel times that may accrue in the future.”

The Department for Transport declined to comment. It said its reasons for granting planning approval were published in its decision letter this month.

• This article was amended on 1 December 2020 to change the main picture to a more recent one.