HS2 is investigating concerns raised by construction firm Mace after a £170m contract was awarded to competitor CH2M.
There had been questions raised over potential conflicts of interest and the role of Roy Hill, HS2's interim chief executive, who was on secondment from CH2M during the procurement process for the contract.
A Mace spokesperson said: “A productive meeting was held with HS2 Ltd last week and they are now investigating our concerns. We look forward to hearing their findings so that we can then consider our next steps.”
HS2 delayed the awarding of the contract last month when Mace wrote to the company for more detail, saying it had postponed the process as "all bidders have confidence in the process".
CH2M was chosen over Mace and its bidding partner Turner & Townsend, and a separate entry by Bechtel.
Last month, Mace said "as a British-owned company" it was "disappointed with HS2's decision" and was mulling its options, including a potential legal challenge.
HS2 met Mace last week to discuss the firm's concerns. City A.M. understands that HS2 has answered some of the queries, and will provide answers to the rest imminently, which will then put the ball in Mace's court as it weighs up whether to pursue a legal challenge if it deems the answers unsatisfactory.
An HS2 spokesperson said: “We’re in discussion with one of the bidders and will make a statement in due course.”
It has said the process involved anonymised bidders and Hill was excluded from attending and receiving minutes from any meetings or discussions during which the procurement might be discussed.
CH2M had already worked on the line as development partner and then as the delivery partner on Phase 1 of the project. Phase 2 spans Birmingham to Manchester and Leeds.
The American firm's European boss Mark Thurston was appointed the new chief executive of HS2 in January and takes over from Hill this month.
The £55.7bn high-speed rail project will cut London to Birmingham journey times by 30 minutes to 50 minutes, with a fleet of trains travelling at more than 200mph.
It was granted Royal Assent last month, with construction set to get under way this year.