Update – 26/05/2015: The transport secretary Patrick McLoughlin has conceded defeat in a legal case brought by campaigners to have the assessment released. To quote The Guardian:
“The report shows that despite government assurances at the time about the costs of HS2, there was private acknowledgement that the quoted budget would have to be increased. The report warned that the £16.3bn budget for the London-Birmingham stretch of the high-speed network was “in danger of being mistaken for the expected cost of Phase 1 – whereas it is only a partial estimate made in 2011 prices with significant exclusions”.

A 2015 high-level MPA report published on Thursday continues to grade HS2 as amber/red – a rating that means successful delivery of the project is in doubt, with major risks or issues apparent. An HS2 insider said: “There’s no doubt it is still in a bad place – but it came from an even worse position.””

Original post

A report by the Major Projects Authority said to contain scathing criticism of the planned High Speed 2 train line was blocked by the Transport Secretary, Patrick McLoughlin.

The publication of the the report under the freedom of information act was blocked by McLoughlin using an unusual veto, last used during the invasion of Iraq. This action was illegal because the report is not an internal government communication.

The HS2 project has since been downgraded to an Amber/Red rating, meaning:- “Successful delivery of the project is in doubt, with major risks or issues apparent in a number of key areas.”