Clearances of ancient woodland for HS2 must be stopped while the project is reviewed unless they are necessary to avoid major costs and delays, Transport Secretary Grant Shapps has announced.

Mr Shapps has ordered HS2 Ltd - the company building the high-speed railway - to assess what 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. "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."

An HS2 Ltd spokesman said: "We are committed to reducing the new high speed railway's impact on ancient woodlands and welcome the announcement by the Transport Secretary today.

"As highlighted by Secretary of State, we must strike a sensible balance between keeping the programme on track and recognising that some works cannot be undone. "We are working with the Department for Transport and our contractors to assess these areas and their impacts while the review is ongoing."

Forty-three of the 52,000 ancient woodland sites in England will be partially affected by the high-speed railway's line between London and Crewe but more than 80% of their total area will "remain intact and untouched", according to HS2 Ltd.

The firm said it is planting more than four times as much new woodland on this route to compensate for the loss of ancient woodlands.

The Woodland Trust charity said at least 108 ancient woods are set to be affected by HS2 as a whole, with 63 suffering "direct loss" and damage due to noise, vibration, changes to lighting and dust. A further 47 are on or near construction boundaries.

Woodland Trust ecologist Luci Ryan said: "This is a welcome step in the right direction for our ancient woodlands, but unfortunately these woods remain threatened as HS2 can still decide for themselves whether works continue or not.

"Until the outcome of the review all ancient woodlands should be off limits full stop. Our welcome is therefore cautious."

Mr Oakervee's review was commissioned by the Government and is analysing whether and how the project should continue.

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.

Mr Shapps published a report by HS2 Ltd chairman Allan Cook which warned that the final phase of the railway may not open until 2040 and the project could cost £88 billion at 2019 prices. 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.

Mr Cook's report stated that phase 1 could be delayed from 2026 until as late as 2031, while the completion of phase 2b could be pushed back from 2033 to 2040.

Transport Minister Baroness Vere told the House of Lords in July that £7.4 billion has already been spent on HS2.

The figure includes money towards the purchase of land and property, ground investigation work, technical designs, IT systems, wages and public engagement.