The firm has been signed up for six months to deliver the review amid soaring delivery costs on the project.

G&T’s appointment comes after HS2’s latest forecasts of costs showed the MWCC element has soared by £6.1bn at 2019 prices.

HS2’s most up-to-date forecast has put main work civils final costs in the range £21.8bn-£23.4bn.

Incoming executive chairman Sir Jon Thompson recently said that 89% of the cost increase from 2020 till now was down to cost plus MWCC contracts alone.

The scope and costs of Phase 1 will now be reassessed following the decision not to proceed beyond the Midlands, including the decision to adopt a development-led approach to Euston.

Thompson has also warned that extra cost pressures loom with the new plans to connect HS2 to the West Coast Main Line through a major redesign at the Handsacre junction, already a choke point on the route.

HS2 and the Government are also at odds about the final cost forecast for phase one with the Department for Transport working on lower figures.

The latest estimate at 2019 prices still does not take into recent rampant cost inflation across the industry, and the Government has now demanded a new cost estimate at today’s prices.