The controversial HS2 railways scheme could be delayed amid concerns of an unrealistic timetable, an official report has claimed.

The National Audit Office (NAO) has warned the high speed rail line between London, Birmingham and the Midlands is facing ‘cost and schedule pressures’ and will cost more than £200m more than originally expected.

According to the report, the first phase is forecast to cost £27,384m, which will exceed available funding by £204m.

The watchdog has also revealed the Department for Transport has asked the company responsible, HS2 Ltd, to look at the impact of extending the timetable for opening its first phase in 2026 by a further 12 months.

‘HS2 is a large, complex and ambitious programme, which is facing cost and time pressures,’ said NAO head, Amyas Morse. ‘The unrealistic timetable set for HS2 Ltd by the Department means they are not as ready to deliver as they hoped to be at this point.

‘The Department now needs to get the project working to a timescale that is achievable.’

The NAO report also raises concerns about whether the total £55.7bn funding packaging will deliver economic growth and regeneration benefits for local authorities along the route.

HS2 Ltd chief executive Simon Kirby said the NAO report ‘recognises the real progress we have made in taking the concept of HS2 and moving it nearer reality’.

‘As the report says, HS2 remains a highly-ambitious project, but as it also demonstrates there are real and substantial grounds why the public, government and parliament should have increased confidence in our ability to deliver the project,’ added Mr Kirby.