Prime minister Boris Johnson has said the government will have to consider the rising cost of the High Speed 2 (HS2) project, but appears to be sending mixed messages as to whether he will give the rail line the green light following an independent review.

Speaking in November on his campaign trail for the snap general election scheduled for 12 December, Johnson hinted that he would approve the project if he wins at the polls. He said: “I’m going to hesitate before simply scrapping something that has been long planned and is of great national importance.

“But we will want to be checking the money is being properly spent and there aren’t ways in which it could be reprioritised or reprofiled.”

However, during a recent interview with LBC, the prime minister commented: “When you’re talking about north of £100 billion it’s only responsible to ask if it’s being sensibly spent.”

A leaked draft version of an independent review of HS2 chaired by Douglas Oakervee suggested the government should push ahead with the project despite its rising cost – originally projected to be £56 billion but now estimated to come in at £88 billion or even higher.

The Oakervee review itself has been mired in controversy, with deputy chair Lord Berkeley claiming his role in the inquiry had finished before the final report was complete. He said he had been given no opportunity to influence the conclusions of the review. Critics have also questioned the impartiality of Oakervee, a former HS2 Ltd chairman.

HS2 is the largest infrastructure project in Europe and the first phase connecting London and Birmingham was originally due to open in 2026. However, new chairman Allan Cook revealed this route might not open until 2028 at the earliest but potentially not until 2031. The schedule for opening phase two – extending the line to Manchester and Leeds – has therefore been pushed back to between 2035 and 2040.

Work has already started on the first phase of the project and will continue until the Oakervee review is published and a decision is made on whether or not construction will go ahead.

The train line will run through Johnson’s constituency of Uxbridge and South Ruislip, which will also be affected by the potential for increased noise from an expanded Heathrow airport, adding pressure on him to scrap the project.

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