Plans to build a tunnel near Stonehenge as part of a scheme to dual the A303 hang in the balance after a landmark court ruling.

The Department for Transport (DfT) granted permission to Highways England (HE) in late-2020 to dual the A303 near the World Heritage Site at a cost of £1.7bn, including a new tunnel through the site itself.

The Save Stonehenge World Heritage Site group took the government to court over the decision, arguing that it had failed to consider the damage to local heritage assets or look seriously at viable alternative schemes.

The whole tunnel scheme is now in doubt after the judge ruled in the campaigners' favour, quashing the planning consent.

Here's what you need to know:

What did the judge say?

SSWHS filed a judicial review against the government, claiming its decision to grant permission for the Stonehenge tunnel was flawed on five counts:

Transport secretary Grant Shapps MP failed to give adequate weight to the impact in individual heritage assets within the site

He "unlawfully" disagreed with the Planning Inspectorate, which advised him to refuse permission for the scheme, and "misconstrued" Historic England's advice in the process

He "adopted an unlawful approach" to considering the extent of harm the scheme would cause to heritage assets

He did not comply fully with the World Heritage Convention

He failed to consider any viable alternatives to the scheme, or take account of how the tunnel scheme may "breach various local policies"

Mr Justice Houlgate noted in his judgement that Mr Shapps had accepted that the road scheme "would have caused permanent and irreversible harm to the World Heritage Site".

He ruled in the campaigners' favour on two of the five counts – the impact on heritage assets and the failure to consider alternative schemes.

He stated in his judgement: "The relative merits of the alternative tunnel options, compared to the western cutting and portals, were an obviously material consideration which the transport secretary was required to assess.

"It was irrational not to do so. This was not merely a relevant consideration which he could choose whether or not to take into account.

"I reach this conclusion for a number of reasons, the cumulative effect of which I judge to be overwhelming."

How have the campaigners reacted?

John Adams, SSWHS director and acting chairman of the Stonehenge Alliance, has expressed his thanks to their legal team and the more than 3,000 people who crowdfunded the court case.

He said: "We could not be more pleased about the outcome of the legal challenge.

"The Stonehenge Alliance has campaigned from the start for a longer tunnel if a tunnel should be considered necessary. Ideally, such a tunnel would begin and end outside the World Heritage Site.

"But 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.

"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."

How has the government responded?

Neither transport secretary Grant Shapps MP nor any of his junior ministers have confirmed whether they will appeal the court's decision.

A DfT spokesman said: "We are disappointed in the judgement and are considering it carefully before deciding how to proceed."

David Bullock, Highways England's project manager for the A303 Amesbury to Berwick Down scheme, said: "We now have to wait while the DfT considers its options.

"We still believe our project is the best solution to the ongoing issues along the A303 past Stonehenge, and was developed after a long and extensive collaboration with our key stakeholders."

Does this mean all work on the Stonehenge scheme will stop?

The short answer is no.

HE intends to continue its procurement process for appointing a contractor for the main body of the work, with an announcement expected in December.

There may be delays in the early, preparatory work on-site – but this is dependent on whether or not the government appeals and how soon any such appeal can be heard.

So while little to no construction work can take place near Stonehenge, preparation behind the scenes will continue in case the government emerges from the appeals process with a victory.

How will this affect the other A303 dualling scheme – and the A358 plans?

The Stonehenge tunnel is one of three major transport schemes HE is pursuing to deliver an unbroken dual carriageway link between the M3 and M5.

The other two are dualling the A303 between Podimore and Sparkford (permission for which was granted in late-January) and dualling the A358 between Taunton and Ilminster.

HE said the court's ruling would not hamper either scheme, since each application was being taken on its own merits rather than a joint package.

A spokesman said: "We remains committed to improving the A303/ A358 corridor, with all schemes being assessed and approved on their own merits.

"The A303 Sparkford to Ilchester scheme works will be starting in September as planned, while the A358 is set for statutory consultation later this year.