Highways England has said it is proceeding with plans to dig a tunnel near Stonehenge, despite the GBP1.7bn scheme being declared unlawful by the high court.

The government-owned company said it would continue to appoint building contracts to ensure the procurement process ran to schedule – although it has paused plans for preparatory work while the Department for Transport “considers its options”.

Campaigners including archaeologists, environmental groups and druids won a high court battle on Friday to stop the controversial project on the A303 in Wiltshire next to the prehistoric monument.

Mr Justice Holgate ruled that Grant Shapps, the transport secretary, acted irrationally and unlawfully when he approved the project. The DfT could still appeal against the decision.

Asked whether it was planning to appeal, a DfT spokesperson said last week: “We are disappointed in the judgment and are considering it carefully before deciding how to proceed”.

David Bullock, the project manager of the scheme for Highways England, said on Wednesday that “the procurement process is very much live”.

He said: “We have to wait while the Department for Transport considers its options, and in the meantime we are continuing with the process to appoint a contractor for the main works phase of the scheme.

“We have now paused our plans to carry out early, preparatory work, but the procurement process is very much live to ensure we maintain programme timescales as best as possible.”

He said they still believed that the project was the “best solution to the ongoing issues along the A303 past Stonehenge” and that it was developed after a “long and extensive collaboration” with stakeholders.

He added: “We are still very much motivated to leave a legacy beyond the road – for Stonehenge, the world heritage site, our local communities and future generations.”

Archaeological fieldwork and preliminary works that were originally planned to start this summer have been postponed.

But three bids have been submitted for the project, with the company expected to announce its choice early in 2022, and a GBP60m contract is due to be awarded late this year to support the construction work’s management.

Shapps gave the project, which includes an overhaul of eight miles of the A303 and a two-mile tunnel, the green light in November, despite advice from the Planning Inspectorate that it would cause “permanent, irreversible harm” to the Unesco world heritage site.

Save Stonehenge World Heritage Site challenged the decision in the high court and won.

Holgate said there was a “material error of law” in the decision-making process because there wasn’t evidence of the impact on each individual asset of the site. Shapps’s failure to consider other schemes was, he said, a breach of the world heritage convention and common law.

Prof David Jacques, who heads the Blick Mead archaeological project, which has made finds that help to tell the story of how ancient humans lived at the Stonehenge site since the ice age, said: “I suspect Highways are putting on a brave face. It would be better if they owned up to the fact that they and the government acted unlawfully and irrationally to push through this vanity project that would have caused proven harm to one of the world’s premier world heritage sites.

“Instead, they are both choosing to save face by continuing to waste money on a scheme which has been entirely discredited by all impartial planning adjudicators. The choice to reduce international aid, for example, yet to still press ahead with feeding this white elephant is a disgrace and will continue to harm Britain’s moral authority in the world.”

Finds at Blick Mead have included perfectly preserved hoofprints of wild cattle, known as aurochs, a mile and a half from the stone circle.

The DfT has been approached for comment.