Ministers are considering slowing HS2 trains as a way to reduce costs after the high-speed rail project ran into delays and ballooning budgets.
The transport department has asked the company building the London-to-Birmingham section to study whether trains could initially operate at a lower top speed.
A formal update on the programme’s timetable and cost is now expected only after the May elections.
Officials say the move is part of a wider review led by Transport Secretary Heidi Alexander, who is weighing a range of measures aimed at saving time and money for taxpayers.
HS2 was engineered to allow trains to travel at about 360 km/h, a design speed well above the maximum used on most British services.
Typical high-speed routes in the UK run closer to 200 km/h, while HS1—the line through the Channel Tunnel—reaches roughly 300 km/h.
Testing trains at the highest speeds would require either a dedicated test track or completion of the full route, steps that officials warn could add years and extra billions to the bill.
One alternative under consideration is carrying out high-speed trials abroad where appropriate infrastructure already exists.
Mark Wild, who previously led the Crossrail project, was hired to rebuild the HS2 programme and produce a realistic schedule and budget.
He had been expected to reveal that the Birmingham leg would miss the 2033 target and that total costs would exceed £100bn in today’s money, but that announcement has been postponed.
Work has already produced major structures such as tunnels and bridges, yet significant construction remains.
Plans for lines north of Birmingham were scaled back, and services toward Manchester are now set to use the existing West Coast Main Line at reduced speeds.
The government has been outspoken about mistakes made under earlier administrations and is under pressure to show value for money.
Political parties were approached for comment on the latest review.
Lowering the operating speed could trim costs and speed delivery, but it will also change the level of journey-time benefits originally promised.
Ministers have yet to decide the path forward.
