The consultation period for the environmental statement of the HS2 high-speed rail project - which is to connect London with Birmingham, Manchester and Leeds - has been extended by an extra 17 days following a ruling by a Commons committee.
Opponents of the £50 billion scheme wanted an extension after 877 pages of documents were initially left off a computer memory stick.
The House of Commons Standing Orders Committee said on Wednesday that the consultation period, due to end on January 24, should be extended until February 10.
Former Welsh secretary Cheryl Gillan, whose Chesham and Amersham constituency lies on the route of the first London to Birmingham phase of HS2, said she was sure campaigners and environmental organisations would welcome the consultation extension.
Stop HS2 campaign manager Joe Rukin said this was the first time the Standing Orders Committee had had to be called in six years.
He went on: "Yet again those in charge of HS2 have been proved to be completely incompetent, only interested in rushing this white elephant through."
A spokesman for HS2 Ltd, the body developing and promoting the project, said: "The Standing Order Committee has ruled in favour of the (HS2) Hybrid Bill's progression and confirmed that it can proceed as planned.
"We are happy to comply with the committee's instruction to extend the Environmental Statement consultation period for a couple of weeks, to allow for full and proper consultation on some pages that were missing from the original material.
"HS2 is the most significant infrastructure project the UK has seen in modern times and a project the country cannot do without."