HS2 Ltd has welcomed a decision by engineering giant CH2M to pull out of a development contract worth up to £170m after rivals raised conflict of interest concerns.

Chairman and CEO of the US-based firm, Jacqueline Hinman, has written to HS2 Ltd chairman David Higgins to formally withdraw interest in the Phase 2b Development Partner Contract award, which was only announced last month.

Reports suggest officials investigated concerns from rival bidder Mace over alleged conflicts of interest after Mark Thurston, regional managing director overseeing CH2M’s European operations, was appointed as the new chief executive for HS2 Ltd.

He is due to start in the spring, 'once he has transitioned his leadership responsibilities at CH2M'.

CH2M said in a statement: ‘The protracted delays and ongoing speculation risk further delays to this critical national infrastructure, thereby increasing costs to UK taxpayers, as well as to the firm.’

A spokesperson for CHSM added: ‘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.’

A spokesperson for HS2 Ltd said: 'As they have announced, CH2M have decided to withdraw from the Phase 2b Development Partner bid process, a decision which we welcome.'

The spokesperson confirmed that the deal was worth £130m -170m. CH2M is also involved in the first phase of the high speed rail link and said it remains ‘fully committed to working with HS2 Ltd on delivering Phase 1 on time and within budget’.

A spokesperson for HS2 Ltd said they had started discussions with the second placed bidder – Bechtel – with a view to signing a contract with them instead.