Boris Johnson has given HS2 the go-ahead, despite fears over its cost and impact on the environment.

The Prime Minister told the House of Commons that his Government had the “guts to take the decision” to deliver prosperity across the country.

To avoid “further blow outs” in HS2’s cost or schedule, a series of measures will be taken to “restore discipline to the programme”, he said.

This will include appointing a minister whose full-time job will be to oversee the project, and changes to the way HS2 is managed.

The announcement follows the completion of a Government-commissioned review by former HS2 Ltd chairman Douglas Oakervee into whether or not the programme should be scrapped.

Mr Johnson said: “The review recently conducted by Douglas Oakervee … leaves no doubt of the clinching case for high-speed rail.

“A vast increase in capacity with hundreds of thousands of extra seats making it much easier for travellers to move up and down our long, narrow country.

“And that means faster journey times, not just more capacity.”

The Oakervee Review found that the final bill for HS2 could reach £106 billion.

It was unable to develop its own estimate of costs but considered that the amount “could be around 15%-20% higher” than figures set out by HS2 Ltd chairman Allan Cook last year.

In a stocktake report, Mr Cook gave an estimate of between £81 billion and £88 billion, compared with a budget of £62.4 billion (both at 2019 prices).

Phase 1 of HS2 will run between London and Birmingham.

A second, Y-shaped phase will launching in two stages: Phase 2a from Birmingham to Crewe, followed by Phase 2b from Crewe to Manchester, and Birmingham to Leeds.

Mr Johnson said the Government will seek to identify where cost savings can be made in Phase 1 without carrying out a detailed redesign.

Before designs for Phase 2b are finalised and legislation is introduced, the Government will “introduce an integrated plan for rail in the North”, he told MPs.

He added: “It will, in line with the findings of the Oakervee Review, look at how we can best design and integrate rail investments across the North including Northern Powerhouse Rail between Leeds and Manchester.”