Parliament’s Public Accounts Committee is concerned the Government has still not decided how phase 2b of the high-speed rail project will integrate with other parts of the rail network and “alarmed by the lack of progress“ on the £2.6bn redevelopment of Euston Station.
In a report, the committee wrote: “Despite Euston being a key part of phase 1, the Department (for Transport) is yet to make key decisions on the design and approach to construction.
“Government also still needs to decide how phase 2b – the northern sections of the route – will integrate with other parts of the railway and transport system.
“Both Euston and phase 2b are complex and risky parts of the programme, but they are critical to the delivery of the promised benefits from High Speed 2. Urgent action is needed if the whole programme is to be delivered on time.”
The current estimated cost of completing HS2 is between £72bn and 98bn (2019 prices), compared to an original budget of £55.7bn in 2015.
But the committee said rising costs have “dented public confidence” in the project and it has “significant concerns” about further costs and disruption.
Dame Meg Hillier MP, chair of the committee, said: “HS2 is already one of the single most-expensive taxpayer-funded programmes in the UK but there’s actually no clear end in sight in terms of the final cost, or even the final route.
“The project was plagued by a lack of planning and transparency from the start and there are many difficulties ahead. This project cannot simply keep sinking more taxpayer funds without greater clarity on the later phases.
“The development of Euston is a real challenge that must be resolved swiftly now.”
Work is well underway on phase 1 of HS2, which links London and Birmingham, and phase 2a, which is due to link West Midlands and Crewe, was approved by Parliament in February.
But HS2 Ltd is waiting for the Government to publish its Integrated Rail Plan before it progress with phase 2b, which is due to link the West Midlands and Leeds and open between 2036 and 2040.
Sir Geoffrey Clifton-Brown MP, deputy chair of the Public Accounts Committee, said: "The overall cost of phase 1 is £35bn with a £10bn contingency, which would appear to be achievable.
“However, plans are not yet complete as to how phase 1 will be integrated into phase 2, and the costs of phase 2a and 2b are far less certain.
"Therefore, the total wide estimate of building the entire railway is far less certain, between £72bn to £98bn, and could well exceed even that."
The Department for Transport said it is making "significant progress with HS2".
A spokesman said: “The project is already supporting more than 20,000 jobs, construction on phase 1 has begun, and MPs have given their backing to the phase 2a route.
"We will continue to rigorously control pressures, and as our latest update to Parliament confirmed, phase 1 remains within budget and schedule.
“The Integrated Rail Plan will soon outline exactly how major rail projects, including HS2 phase 2b, will work together to deliver the reliable train services that passengers across the North and Midlands need and deserve."