Work on the £1.7bn Stonehenge Tunnel has been put on hold after campaigners were granted permission to challenge the ruling that the project should go ahead.
National Highways, which had hoped to begin preparatory work on the site this month, said it was “hugely disappointed” by the court’s decision to allow the appeal.
A date for the hearing is still to be set, but it is expected to take place before the summer.
Plans for the A303 Amesbury to Berwick Down scheme would see a 3.2km tunnel built under the Stonehenge World Heritage Site and 12.8km of dual carriageway between Amesbury and Berwick Down.
The Save Stonehenge World Heritage Site (SSWHS) campaign group had been seeking a judicial review of the project’s development consent order.
In February, the High Court threw out the case brought by the group.
Rejecting all grounds for challenge raised by the campaigners as “unarguable”, Mr Justice Holgate refused permission to apply for judicial review.
But in the latest twist in the long-running legal saga, SSWHS has now been allowed to challenge that decision in the Court of Appeal.
Lord Justice Lewison said the grounds for appeal raised by the group had “real prospects of success”.
He added that the scale of public interest in the proposed scheme gave rise to a “compelling reason” for the Court of Appeal to hear the appeal.
“The question of improvement of the A303 is of national importance and has been a long time in the planning,” he said.
“The appeal should therefore be expedited, to be heard if possible before the long vacation.”
A303 Stonehenge project director for National Highways David Bullock said the ruling represented a setback for the project.
“We are hugely disappointed by this decision, which will cause more delays to this scheme as the next stage of the legal process unfolds,” he said.
He said National Highways would participate fully in any future legal proceedings to continue to present the case for the scheme, working closely with the Department for Transport.
SSWHS director John Adams said the ruling was “extremely good news”, describing the project as “incredibly damaging” to the Stonehenge World Heritage Site.
“All those who care passionately about our cultural heritage can breathe a sigh of relief,” he said.
“We now have a new opportunity for the government decision to be thoroughly scrutinised.”
