HS2's future is further in doubt today after the felling of swathes of trees along the route was suddenly halted.
Clearances of ancient woodland for the multi-billion pound line connecting London, Birmingham and northern cities must be stopped unless they are necessary to avoid major costs and delays, Transport Secretary Grant Shapps has announced.
It is the biggest hint yet that the scheme could be dropped.
Mr Shapps has ordered HS2 Ltd - the company building the high-speed railway - to assess what tree removals can be halted until after the inquiry led by the firm's former chairman Douglas Oakervee is completed.
All other preparatory works will continue during the review.
Mr Shapps said: 'There is no sense in hiding the challenges HS2 faces, or masking the difficult decisions that need to be taken.
HS2, which would look like this between London and Birmingham, could be scaled back or cancelled as the felling of woodland was stopped
Trees in forests on the route from London to Birmingham (pictured in the Chiltern Hills near Great Missenden) and beyond will be saved 'unless they are necessary to avoid major costs and delays'
'So, as Douglas Oakervee's review continues, we must take a sensible approach and recognise that some works simply cannot be undone later.
'Having listened to the concerns of affected residents and parliamentary colleagues, I have ordered HS2 Ltd to consider what works affecting ancient woodland clearances can be delayed for the duration of the review.
'This ensures we avoid irreversible decisions without major impacts on cost and schedule.
'HS2 may be a complex project overall but I think this request is just common sense.'
Mr Oakervee's review was commissioned by the Government and is analysing whether and how the project should continue.
Transport Secretary Grant Schapps has hinted that HS2 could be killed off - but insists no final decision has been made
It is considering a number of factors including the project's benefits, impacts, affordability, efficiency, deliverability, scope and phasing.
The final report will be completed in the coming months and will inform the Government's decisions on next steps for HS2.
It emerged earlier this month that the project could be delayed by up to seven years and run £26 billion over budget.
Phase 1 of HS2 is planned to run between London and Birmingham.
A second Y-shaped phase will launch in two stages: Phase 2a from the West Midlands to Crewe followed by phase 2b from Crewe to Manchester, and Birmingham to Leeds.
Last week Tory MPs urged the prime minister to scrap the HS2 ‘white elephant’ last night after it emerged it is running up to up to £32 billion over budget and seven years late.
Pictured is the HS2rail route, showing phase one (dark blue line), two A (light blue line) and two B (orange line) as well as existing services that will use the network (yellow line)
Amid growing speculation about the soaring costs of the high speed rail link, Transport Secretary Grant Shapps published a searing assessment by HS2 Ltd’s new chairman, Allan Cook.
HS2 in numbers
£7.4billion: Amount spent since HS2 Limited set up in 2009. Including £2.6billion spent last year
Zero: Length of track that has been laid
£56billion: official budget for entire project
£33billion: original budget
£81-£88billion: Latest estimate, adjusted for inflation
318 employees - almost a quarter of workforce- paid at least £100,000. This includes 115 paid more than £251,000
£651,488: annual pay package of chief executive Mark Thurston. Included £46,000 bonus
60 minutes - predicted journey time saving between Manchester and London compared with the fastest existing services.
350,000 - trees to be planted along the route between London and Birmingham by HS2 Ltd.
225mph - planned top speed of the trains
The report - slipped out on a tumultuous day in Westminster - concluded that both the budget for HS2 and timetable for building it were ‘unrealistic’ from the start.
Mr Cook said he did not believe the new railway line could be delivered within its official £55.7 billion budget, which is based on 2015 prices.
Instead he predicted that the true cost was likely to range between £72 billion and £78 billion, again based on 2015 prices.
Telling MPs he wanted to provide them with the ‘full picture’, Mr Shapps said this was equivalent to between £81billion and £88billion when adjusted for inflation.
The original budget for the rail line when work began a decade ago was £33billion.
Mr Cook also said the timetable for delivering HS2 was also not ‘realistic’.
He predicted that the entire line connecting London with Birmingham and onward to Northern cities including Manchester, Leeds and Sheffield may not be fully completed until 2040 - seven years later than officially scheduled.
He also recommended an opening date of between 2028 to 2031 for phase one between London and Birmingham, up to five years later than the planned 2026 opening date.
Mr Cook was adamant that ‘HS2 remains the right strategic answer to join up Britain more effectively to meet the transport needs of the 21st century’.
He also said the ‘transformational benefits it will deliver for the country’ had been underestimated when the project was conceived.
But he said the original plans did not take ‘sufficient account’ of building a high speed railway through a ‘more densely populated country with a more difficult topography than elsewhere’.
In a written statement to the Commons, Mr Shapps hinted that HS2 could be cancelled.
He said while he and the Prime Minister support transport investment, they have been clear that the ‘benefits of big infrastructure projects must stack up’.
He added: ‘I want the House to have the full picture. There is no future in obscuring the true costs of a large infrastructure project - as well as the potential benefits.’