The government is expected to “broadly back” HS2, the high-speed rail project which would cost around £106bn, despite opposition from Conservative backbenchers.

Boris Johnson is set to hold crunch talks later today with Chancellor Sajid Javid and Transport Secretary Grant Shapps, ahead of the expected final decision to back the scheme. The high-speed rail will link London, Birmingham, the East Midlands, Manchester and Leeds.

Over 9,000 people are currently working on the project, many of them on the Euston to Old Oak Common section of the line in the capital, where construction work is already well underway.

The Prime Minister told the Commons on Wednesday: “I just want to reassure all 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.”

The scheme has been met with significant criticism, especially in regard to the spiralling costs and environmental impact HS2 would have.

A leaked report suggested the project could cost almost double the £56bn expected in 2015. The report, which was leaked to the Financial Times, said that there was a “considerable risk” that costs would rise by another 20%.

Whitehall’s spending watchdog stressed earlier this month that the risks and the complexity of the HS2 project have been under-estimated. The National Audit Office warned it was impossible to “estimate with certainty what the final cost would be.”

Boris Johnson’s top aide, Dominic Cummings, and his transport adviser, Andrew Gilligan have warned that the project would be a waste of money. Several environmental groups have argued the money is better invested elsewhere as HS2 could cause huge damage to natural habitats and ancient woodlands.

However, business chiefs in the north of England have argued that HS2 is key to boosting transport links in the region and can reduce overcrowded trains. Andy Street, mayor of the West Midlands, believes HS2 to be “critical to the revival of the West Midlands economy.”

Speaking about the project on ITV’s Peston programme, Grant Shapps claimed that HS2 would be “the biggest investment, biggest infrastructure project possibly in the world, certainly in Europe, and the public would expect us to look carefully at it.”

The first phase of the rail line between London and Birmingham is expected to open by the end of 2026 and the second phase, Leeds to Manchester is scheduled to have been completed by 2033.