The first stab at what the true cost of delaying works to control day-to-day project costs has emerged in leaked internal Government documents.

The briefing also warns the two-year pause to construction work on key sections at Euston and phase 2a between Birmingham and Crewe will actually set work back 3.5 years when taking into account re-mobilisation to full capacity.

Earlier this week, rail minister Huw Merriman admitted that the cost of rebuilding Euston had risen by £2.2bn to £4.8bn.

In his report on the project he also warned that the Euston terminus was not affordable at that price.

The industry has always argued that a project delay could only ever inflate the delivery budget even if it buys time to revisit the costly Euston terminus design for a third time to re-engineer down costs.

A spokesperson for the High Speed Rail Group, representing suppliers and contractors, said: “As we said when the two-year delay was announced in March this year, the cheapest way to deliver HS2 is quickly. 

“Once complete the railway will be a vital new artery for the United Kingdom which adds necessary capacity for people and goods, while getting passengers off planes and onto trains.

“This is necessary both for economic growth and to meet the UK’s net zero ambitions.

“We need ministers to urgently agree a long-term plan to deliver this vital piece of infrastructure.”