A group of MPs says the government is running out of time to deliver the HS2 rail link serving South Yorkshire.
There are fears that plans to build the high-speed line from Birmingham to Leeds could grind to a halt due to escalating costs and delays.
The Public Accounts Committee said the government is providing a clearer explanation of costs than previously seen, but is "increasingly alarmed" about key elements of the programme nationally - specifically what the MPs describe as a lack of progress at Euston Station.
The group said the 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.
Members said the current estimated cost of completing HS2 is between £72 billion and £98 billion, compared to an original budget of £55.7 billion in 2015.
The Chair of the Public Accounts Committee, Dame Meg Hillier MP, 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.”
Responding to the committee's concerns, the government said it is making significant progress.
A Department for Transport spokesperson said: “We are making significant progress delivering HS2, a key part of our promise to build back better from Covid-19. We welcome the committee acknowledging that progress and our renewed commitment to transparency.
“The project is already supporting more than 20,000 jobs, construction on Phase One 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 One 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.”