The Court of Appeal today dismissed all appeals brought against the Department for Transport's (DfT) decision to progress with High Speed 2 (HS2) by an alliance of 15 local authorities, HS2Action Alliance and Heathrow Hub Limited.

The decision gives the green light to the £50bn London to Birmingham, Manchester and Leeds route, although the local authorities have requested the chance to appeal once more to the Supreme Court.

A further appeal will centre around a divided decision by the three appeal judges today on the issue of whether the Government should have carried out a full Strategic Environmental Assessment (SEA) to assess the effect on the environment of both HS2 and its alternatives.

While the master of the rolls, Lord Chief Justice Dyson and Lord Justice Richards supported the DfT's contention that no SEA was required as HS2 was not a 'plan or programme', Lord Justice Sullivan disagreed.

Lord Justice Sullivan said: ‘If, as I have concluded, an SEA is required and there has not been substantial compliance with the SEA Directive, it would be difficult to think of a more egregious breach of the directive given the scale of the HS2 project and the likely extent of its effects on the environment.'

Cllr Martin Tett, chairman of the anti-HS2 51m alliance and Buckinghamshire CC leader said: ‘We are disappointed with the result. On four grounds brought to the Court of Appeal by the local authorities, the appeal judges found against us on the technicality that in theory Parliament is not bound by any decision of the Government and could chose to reject or amend the project.

‘This is another example of the Department for Transport and HS2 Ltd riding roughshod over public opinion, ploughing ahead regardless of what local communities want and ignoring the environmental merits of the alternatives. We have evidence that our alternative to HS2 would provide all of the capacity required, far more quickly, at a fraction of the cost and would be less damaging to the environment.'

The local authorities have asked for permission to appeal to the Supreme Court - the highest court in the land - on the SEA ground and an additional related ground that the Hybrid Bill process for the scheme is incompatible with another aspect of European law, the Environmental Impact Assessment Directive.

High speed rail minister Simon Burns said: 'By dismissing all grounds of appeal and declining to refer the case to Europe, this is the second time in four months a court has rejected attempts to derail HS2.

'Parliament is the right place to debate the merits of HS2, not the law courts, and we will introduce the hybrid bill for Phase One before the year is out. I urge opponents not to waste any more taxpayers' money on expensive litigation and instead work with us on making HS2 the very best it can be.'

The Government will be moving forward as planned with introducing legislation in Parliament later this year and getting the scheme ready for construction in 2017, he added.

Phase One of the scheme is set to open in 2026, with the full Y-shaped route open in 2032/33.