Transport Secretary Grant Shapps approved the Amesbury to Berwick Down upgrade last November against the advice of planning inspectors, prompting a judicial review challenge to be brought by campaign group Save Stonehenge World Heritage Site.

High Court judge Mr Justice Holgate concluded that the decision to grant consent was unlawful after agreeing with the group’s argument that the Secretary of State did not properly assess the impact of the project on each heritage asset within the site.

The judge also ruled that Grant Shapps made an error of law by failing to consider alternatives to the scheme such as a longer tunnel, which may have been less damaging to the world heritage site.

The judicial review outcome marks a major set back for the £1.7Bn project and has been described as a disappointment by the Government, sub national transport body Peninsula Transport and Historic England.

A Department for Transport spokesman said: “We are disappointed in the judgment and are considering it carefully before deciding how to proceed.”

Peninsula Transport chair Andrea Davis said: “We remain firmly of the view that the A303 Stonehenge scheme is essential to delivering much needed improvements to the A303 / A358 / A30 corridor.

“The investment for this scheme is essential to the economic performance of the South West peninsula,” she added, and urged the Government to ensure that lessons are learned quickly from the ruling.

A Historic England spokesman said: “We believe that the scheme had the potential to deliver a lasting positive legacy for the World Heritage Site.

“This is a missed opportunity to remove the intrusive sight and sound of traffic past the iconic monument and to reunite the remarkable Stonehenge landscape, which has been severed in two by the busy A303 trunk road for decades.”

Meanwhile Save Stonehenge World Heritage Site’s director John Adams said the group “could not be more pleased” about the outcome of its legal challenge. “Now that we are facing a climate emergency, it is all the more important that this ruling should be a wake up call for the Government,” he added.

“It should look again at its roads programme and take action to reduce road traffic and eliminate any need to build new and wider roads that threaten the environment as well as our cultural heritage.”

(Photograph: Highways England)