The cost of HS2 came under fire recently after a Government-commissioned review found the project could end up costing up to £106 billion.
A widely-leaked inquiry led by former HS2 Ltd chairman Doug Oakervee reportedly found there is "considerable risk" the high-speed rail project's cost will rise by up to 20%.
It came just a few weeks after the deputy chairman of the now-defunct review panel, Lord Tony Berkeley, criticised HS2 for being "completely out of control financially".
The current HS2 Ltd chairman Allan Cook published a report just four months ago which set out an estimated cost range of between £81 billion and £88 billion.
Transport Secretary Grant Shapps promised a decision on HS2 would be made "very soon", with expectations of a go-ahead increasing after Chancellor Sajid Javid threw his weight behind the project.
But Tory MPs threatened a rebellion after the news that approval from Cabinet looks imminent, with MP for Buckingham Greg Smith saying he would vote against the scheme.
HS2 was allocated £56 billion in 2015. It's been a number of years since the project was given the green light, and while phase one was initially planned to launch in 2026 a recent report by HS2 Ltd said this would be pushed back until 2031.
The Standard takes a look at how much has been spent on the project so far and what the proposed route is:
What is the proposed HS2 route?
Phase one of HS2 is planned to run between London and Birmingham, with phase 2 to run in a Y-shaped route, one from Birmingham to Leeds and the other route from Birmingham to Manchester.
The initial plan was for the lines to carry 400m-long (1,300ft) trains of up to 250mph, with each train having as many as 1,100 seats, potentially trebling passenger numbers between the cities.
The line, linking London, Birmingham, Manchester and Leeds on one route, is said to slash journey times by half.
Phase one of the route will start at London Euston before running through the north west of the capital.
It will then cut through rural areas of the UK, such as Buckinghamshire and parts of the Midlands, before ending up in Birmingham.
How much has been spent on HS2 so far?
Billions of pounds have already been spent on the project since it was first launched.
Lord Berkely released a report early in January in which he hit out at the ever-increasing costs of the ambitious rail project, saying independent analysis suggests it could end up costing at least £107.92bn.
Among several grave concerns listed in the report was the blow-out of estimated costs - while the project was initially expected to cost £50.1billion, latest estimates by HS2 LTD put the price at £88 billion.
Lord Berkeley however has said independent analysis arrives at a figure of at least £107.92 billion. During the election last year, Boris Johnson said he expected the figure to rise above £100bn.
According to the Guardian, by September last year around £7.5bn had already been spent on the project thanks to preparatory work in London and Birmingham, which included demolitions and buying properties along the route.
However the Government-commissioned inquiry led by Mr Oakervee found the project could end up costing as much as £106 billion.
Mr Oakervee's review recommends that work on phase 2b of HS2 from the West Midlands to Manchester and Leeds should be paused for six months to investigate if it could be a mix of conventional and high-speed lines, according to the Financial Times, which has seen a copy of the paper.
The review concluded that the Government should "on balance" continue with the 250mph railway, which would initially go from London's Euston station to Birmingham and then to Leeds and Manchester by 2040, but that this is subject to "a number of qualifications".
A decision on whether to go ahead with the project will be made in "weeks rather than months", Transport Secretary Grant Shapps said.
When is HS2 expected to launch?
The railway was always due to open in stages, with phase one initially expected to launch in 2026 and the final section from Crewe to Manchester and Birmingham to Leeds completed by 2033.
However, a report by HS2 Ltd chairman Allan cook said the original plans "did not take sufficient account" of the effect of building a high-speed line through areas that are densely populated and with challenging ground conditions.
Instead, phase one could be opened as late as 2031 with Phase 2b, the full high-speed line to Manchester and Leeds, potentially facing an opening date of between 2035 and 2040.
