Sir David Higgins, HS2 chairman, said the body would now tighten up disclosure procedures after US consultant CH2M withdrew from a preferred development partner role on the second phase of HS2.

He revealed the move to tighten up bid requirements as he was quizzed by the Transport Select Committee about events leading up to CH2M being selected as preferred contractor.

CH2M had faced conflict of interest allegations from rival bidder Mace, after HS2’s former chief of staff Christopher Reynolds produced lessons learnt documents from phase one to inform the second phase development partner tender process.

After leaving HS2 last June, Reynolds went to work for CH2M in September.

Higgins said that HS2 had no evidence that Reynolds had influenced CH2M’s bid. But despite this CH2M withdrew “for their own reasons”, revealed Higgins.

HS2 now intends to rewrite bid documents to force contractors and consultants to name all people involved in the bidding process.

He said conflict of interest clauses would be strengthened as part of the due diligence process.

“We do intended to tighten it up following this exercise. In future we will say you need to disclose to us who you intend to use on your tendering.

“It will give us more of a chance to be able to scrutinise this ourselves.”

He added: “It is something we will tighten in our tendering process – but this tendering process is standard practice, it’s used on every major engineering and civil contract to date.

“I have to say with the publicity that surrounds this, there would not be a contractor or engineering firm in the UK now that will not be very focused on declaring conflict of interest.”

Higgins also confirmed that second placed Bechtel would now be awarded the contract after its bid came in 15% cheaper than third placed Mace.

In a statement after the hearing, a Mace spokespersons said: “As the Transport Select Committee has shown there are a lot of serious questions to be answered around HS2’s procurement process.

“If we hadn’t raised these concerns, these serious issues would never have come out.”

“David Higgins admitted that HS2 needs to tighten up their process is an admission that the procurement was seriously flawed.

“It’s remarkable that he also admitted that if CH2M hadn’t withdrawn, they would have been sacked – which is a clear admission that their procurement process was riddled with errors.

“Over the past 26 years we have bid on thousands of projects, but we have never yet taken a case to the High Court. This tells you how seriously we take the matter.”