THE fight against HS2 is set to go to Europe, with a Bucks-based action group planning to launch a further appeal.
Judges at the UK's highest court found the government had not contravened any law by failing to carry out a Strategic Environmental Assessment of the project.
But members of the HS2 Action Alliance disagreed with the verdict and have announced their intention to potentially fight the court decision at the European Court of Justice.
The Amersham-based campaign group - one of three to bring the court action - say the judges' refusal to refer the matter to the European court is in breach of its obligations under the EU's Aarhus Convention.
The Convention rules public authorities should make arrangements to "enable the public affected and environmental non-governmental organisations to comment on proposals for projects affecting the environment, or plans and programmes relating to the environment".
Members of the HS2 Action Alliance say this was not done - and now plan on bringing complaints to the Aarhus Convention Compliance Committee and the European Commission.
If either complaint is upheld, the matter will be considered by the European Court of Justice.
The HS2 Action Alliance said the Supreme Court decision had "obvious EU-wide implications".
Group director Hilary Wharf said: "We always knew this would be a long fight. A number of the judges, led by Lady Hale, thought long and hard about whether the issues HS2AA raised should be referred to the European Court of Justice.
"This and the fact that we were given right to appeal to the highest court in the land shows how seriously the need for an Strategic Environmental Assessment should be taken.
"We will continue to press the government to meet its environmental obligations. The government should be safeguarding our environment for future generations and the simple fact is HS2 is an unnecessary and hugely damaging project environmentally."