The move follows a storm of controversy following the contract award last month.

Beaten bidders led by Mace raised questions over the award.

The concerns followed the appointment of CH2M European managing director Mark Thurston as HS2’s new chief executive just two weeks after the contract award.

CH2M managing director Roy Hill was also seconded to HS2 as interim chief executive last October – months before the contract award.

CH2M wrote to HS2 Chairman David Higgins today confirming its decision to withdraw from the Phase 2b Development Partner Contract.

A spokesperson for CH2M said: “CH2M today provided formal notice to HS2 Ltd that we are withdrawing our interest in the HS2 Phase 2b contract.

“CH2M has demonstrated all appropriate measures taken throughout to ensure the integrity of the procurement process.

“Notwithstanding these efforts, we have taken the decision to alleviate any further delays to this critical national infrastructure project which could ultimately lead to increasing costs to UK taxpayers, as well as to our firm.

“CH2M’s reputation reflects excellence earned by placing the interests of our clients and communities first, best exemplified by our delivery of vital programmes like Crossrail, the London 2012 Olympics, the most sustainable to-date; HS2 Phase 1; and the Thames Tideway and Lee Tunnels.”

Bechtel is now believed to be lined-up as a replacement.