Chancellor Sajid Javid is set to throw his support behind HS2 ahead of a key meeting with Boris Johnson and Transport Secretary Grant Shapps.
It is understood that having reviewed costs and alternatives the Chancellor will “broadly back” the high-speed line from London to Birmingham, Manchester and Leeds.
Downing Street declined to rule out that Mr Johnson could overrule Mr Javid on the infrastructure project, with the Prime Minister’s official spokesman saying: “It’s an important decision that will be taken based on the facts and we will announce it when we are ready.”
Mr Shapps has insisted that no decision on the controversial infrastructure project – the biggest in Europe – will be announced this week.
It has been estimated the scheme, which was allocated £56 billion in 2015, could cost up to £106 billion.
Decision on HS2 is coming
The Prime Minister told the Commons on Wednesday that a decision on the project would be made “very shortly”.
He said: “I just want to reassure all of my honourable friends and everybody, whatever persuasion they may be about HS2 across this Chamber, that there will be an announcement and a decision very shortly.”
Some £8 billion has already been spent on the scheme.
The meeting comes as Mr Javid has put pressure on Cabinet colleagues to identify where cuts of 5% could be made in their departmental budgets.
In a letter, co-signed by Mr Johnson, the Chancellor urged ministers to identify projects that could be abandoned ahead of his first Budget as Chancellor in March.
The intervention was seen at Westminster as a bid to find resources to fund Tory election promises on infrastructure, health and law and order.
Impossible to estimate final cost
Whitehall’s spending watchdog said this month that HS2 is over budget and behind schedule because its complexity and risks were under-estimated.
The National Audit Office (NAO) warned that it is impossible to “estimate with certainty what the final cost could be”.
Phase One between London and Birmingham was due to open in 2026, but full services are now forecast to start between 2031 and 2036. It is designed to carry trains capable of travelling at 250mph (402km/h).
Business chiefs in the north of England have argued that pushing forward with HS2 is key to boosting transport links across the region and providing increased capacity on the overcrowded rail network.
Construction firms warn that scrapping it would cause major damage to the industry.
However, opponents insist HS2 is too expensive and the money would be better spent elsewhere, while several environmental groups say it would cause huge damage to natural habitats and ancient woodland.
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