MPs also monitoring row over controversial tender after CH2M walked away from 拢170m deal last week

Mace is still considering legal action against HS2 over the controversial bidding process for a 拢170m role on the megaproject, after crunch talks between the firm and HS2 Ltd ended without agreement on Friday.

Pressure mounted further over the weekend as the chairs of two scrutiny committees of MPs - public accounts and transport - told the Telegraph they were monitoring the issue.

US consultant CH2M - which had been picked by HS2 Ltd as development partner for the second phase of the line branching north of Birmingham to Manchester and Leeds - dramatically walked away from the deal last Wednesday.

CH2M鈥檚 decision came after losing bidder Mace raised a series of questions about the process with HS2 Ltd after hiring 拢650 an hour QC Michael Bowsher, including over alleged conflicts of interest arising from an exchange of senior staff between the two organisations.

A source close to Mace claimed HS2 鈥渟eem dead set on defending a seriously flawed process鈥.

Mace wants HS2 Ltd to re-run the tender process. However, HS2 Ltd鈥檚 preference is to award the deal to second-placed bidder Bechtel, potentially as early as this month, to avoid further delays to the project.

A Mace spokesperson said: 鈥淲e continue to look closely at our options, and remain hopeful that HS2 will come to their senses鈥

鈥淚n 26 years of working on some of the most iconic projects around the UK and the world, we have never yet taken a case to the High Court, and would not take any decision lightly.鈥

好色先生TV reported on Friday that QC Michael Bowsher told senior Mace figures that HS2 has a case to answer over its handling of the process for a 拢170m contract on the second phase of the rail link.

Mace has alleged there were conflicts of interest after HS2 Ltd, which is responsible for building the network, appointed CH2M European managing director Mark Thurston as its new chief executive earlier this month. He replaced interim Roy Hill, who was himself seconded to the client from CH2M, while another senior figure at HS2, its former interim chief of staff Christopher Reynolds, who spent five years at HS2, joined CH2M last year in a technical support role.

But Mace has said it has other concerns beyond this, with a spokesperson confirming last week: 鈥淚t鈥檚 important to note that conflicts of interest was only ever one element of our concerns.鈥

A HS2 spokesperson said: 鈥淲e have no plan to re-run the contest and have started discussion with the second-placed bidder - Bechtel鈥 Our chairman, David Higgins, would be happy to answer questions in front of any relevant parliamentary committee.鈥

Meanwhile in its statement last week, CH2M, which has its London office in Hammersmith, said HS2 were 鈥渁ware of the involvement of Mr Reynolds throughout the procurement process, as documented in CH2M鈥檚 bid, which expressly identified Christopher Reynolds and included quotes from him鈥.

It added: 鈥淐H2M is clear that it went above and beyond the conflict of interest protocols, as set out by HS2 Ltd.鈥

A source close to CH2M said the firm had not been put under pressure from Whitehall to back out of the deal. 鈥淭here was zero contact between the Department for Transport and CH2M.鈥

CH2M, which is carrying out a similar role on the first phase of HS2, is believed to have withdrawn from the bid after deciding sticking with it no longer made commercial sense. 鈥淭hey took the commercial decision they didn鈥檛 want to be dragged along with this anymore.鈥