Transport secretary Patrick McLoughlin revealed the revised figures today after the Chancellor had barely sat down from putting the project at the heart of the Government’s new £100bn infrastructure plan.

The revelations came as MPs debated a second reading of the High Speed Rail (Preparation) Bill, which will allow the Department for Transport to get the project up and running.

The first phase is now budgeted at £21.4bn and the second phase at £21.2bn, and includes a £14.4bn contingency fund across the scheme.

McLoughlin added that he expected the final cost to be below the sum set aside and pointed out the Olympics also came in under budget.

The increased costs cover changes to the route, including a tunnel under the M6 at Birmingham, as well as the increased contingency fund.

The eventual vote went 325 to 37 in favour of the new railway progressing.

The Bill gives the Government greater funding powers to enable the project to move into the detailed planning stage towards the end of the year.