The procurement process is expected to last 18 months for the £1.7bn scheme.

The first OJEU notice covers the £1.25bn main works contract for the construction of the tunnel’s civil, structural, mechanical, electrical and technology components, including the tunnel boring machine, along with the approach roadworks and structures.

Contracts for enabling preliminary work will be procured separately, as part of the total £1.7bn capital cost of the scheme.

The procurement model is through competitive dialogue allowing a period of design development and discussion during the tender phase when solutions are developed and tested prior to awarding a contract.

Highways England said the approach “allows greater flexibility with the appointed team able to hit the ground running once the contract is awarded.”

Upgrade work on the A303 between Amesbury and Berwick Down includes:

• eight miles of free-flowing, high-quality dual carriageway
• a tunnel at least two miles long underneath the World Heritage Site, closely following the existing A303 route, but a further 50 metres away from the Stonehenge monument, avoiding important archaeological sites, and avoiding intrusion on the view of the setting sun from the stones during the winter solstice
• a new bypass to the north of the village of Winterbourne Stoke
• junctions with the A345 and A360 either side of the World Heritage Site

Highways England Project Director Derek Parody said: “We expect this scheme to be of interest to some of the world’s best construction companies, who want to be part of delivering this transformational project – a scheme which will not only unlock congestion along this vital A303 route, conserve and enhance the Outstanding Universal Value of the World Heritage Site but also benefit the local and regional economy by providing skills and job opportunities for businesses large and small.

“This in no way pre-empts the outcome of the ongoing Development Consent Order Examination.

“While this continues to progress, we need to begin the procurement to put us in a position to be able to start construction on schedule in 2021, providing consent is given.”

Contractors interested in more details of the procurement process should go to Highways England’s procurement portal Bravo.