Britain's new high-speed railway linking London with other major English cities will open years late and cost an extra £20 billion ($24 billion, 22 billion euros) to build, the government warned Tuesday.
The Department for Transport announced that the cost of building High Speed 2 (HS2) has escalated due to the complexity of building in densely populated cities and challenging ground conditions.
The budget has surged to between £81-88 billion, up from the prior guidance of £62.4 billion, according to inflation-adjusted figures given on Tuesday.
And rather than HS2's first phase opening in 2026, trains face not running until between 2028 and 2031, the government added.
The revised forecasts were made by HS2 chairman Allan Cook to transport minister Grant Shapps.
They come ahead of findings into a review ordered by Prime Minister Boris Johnson into the huge infrastructure project.
"The prime minister and I have been clear about the potential for transport investment to drive growth, redistribute opportunity and support towns and cities across the UK," Shapps said in a statement.
"But we have been equally clear that the costs and benefits of those investments must stack up."
The first phase of HS2 plans to connect London in southeast England with the country's second biggest city Birmingham in the Midlands.
The second phase is for trains to travel further north to cities Manchester and Leeds.
Originally planned to open in 2033, this section of track now risks being delayed until between 2035 and 2040.
Johnson has previously warned that HS2 would end up costing more than £100 billion -- but also signalled that the project would continue following costly construction work already through Britain's countryside and after the review that could see alterations to the high-speed link.
The review will be led by former HS2 Ltd chairman Douglas Oakervee and report back before the end of 2019.