A verdict on Highways England’s controversial A303 Amesbury to Berwick Down scheme in Wiltshire was originally due to be reached by 2 April, but was delayed until 17 July to allow further work to be carried out and will now be made in November.

Transport Minister Andrew Stephenson said in a statement: “Following notification of a recent archaeological find within the World Heritage Site, the deadline for the decision is to be further extended to 13 November 2020 (an extension of four months) to enable further consultation on and consideration of this matter before determination of the application by the Secretary of State.”

He added that the decision to set a new deadline is without prejudice to the decision on whether to give development consent.

Salisbury MP John Glen said the announcement will come as unwelcome news to local residents, who “had hoped that we were finally moving forward after many years of debate on the issue”.

Writing on Twitter, he said: “Stonehenge is a unique heritage asset with a global profile. The final decision must weigh up all evidence and consider every angle. I remain hopeful the green light will be given in November.”

Wiltshire Council’s cabinet member for highways Bridget Wayman agreed that deferral of a decision about the road upgrade will not be welcomed by some local residents, but added it is important that correct processes are followed.

“This scheme will bring many benefits for the ancient monument, helping to return the Stonehenge landscape to something like its original setting, while also improving the lives of local people and bringing more reliable journeys to users of the A303,” she said. “It will represent a significant investment in Wiltshire that will boost the south west economy, unlocking jobs and investment throughout the entire region.”

One of the leading archaeologists behind the recent find – a Neolithic ring of at least 20 deep shafts – described the A303 upgrade as “an act of monumental vandalism”.

University of Bradford chair in landscape archaeology Professor Vince Gaffney said: “Stonehenge sits within a world heritage landscape with hundreds of archaeological monuments that are inherently linked to the iconic site itself. The current proposal for the A303 will undoubtedly remove the unsightly road, but it will gouge a way through a unique landscape.

“Whether the archaeological mitigation or the scheme is adequate is debatable; whether it will harm Britain’s premier archaeological landscape is unquestionable.”

Earlier this year the National Audit Office questioned the viability of the proposed dual carriageway upgrade to the A303 – which includes a 3km tunnel beneath Stonehenge – in terms of cost, timescale and likely benefit.

Highways England said the recent archaeological find is in the north east corner of the World Heritage Site, well outside the scheme boundary. “We are confident that the proposed scheme presents the best solution for tackling a longstanding bottleneck on this section of the A303, creating more reliable journeys, while returning the Stonehenge landscape to something like its original setting and helping to boost the south west economy,” the company said.

Photograph: Highways England