The Supreme Court will hand down its decision tomorrow morning (Wednesday) on the appeal over the HS2 hybrid bill procedure.
The judges will announce at 9.45am whether the HS2 Action Alliance plus a group of councils – one of them Hillingdon – Bucks County Council and Heathrow Hub have convinced them that the government should have carried out a full environmental impact survey before making the decision to press ahead with the high speed line.
Last July, the Court of Appeal largely rejected the groups' multi-stranded appeal over the outcome of the judicial review into HS2, but it did allow a challenge in the Supreme Court over the environmental impact statement.
Then on Tuesday the House of Lords Select Committee on Standing Orders decided to punish the government and HS2 Ltd for not correctly distributing the statement as part of the hybrid bill published last November.
It directed that the consultation period on the environmental impact statement must be re-set, starting from January 2 and ending on February 27.
This might give anti-HS2 campaigners fresh heart ahead of tomorrow's ruling.
They will be hoping the cumulative effect of the rulings will knock the passage of the bill through Parliament off schedule. It is already thought the Lords' decision could threaten the chances of a second reading by the Easter recess.
Joe Rukin of Stop HS2 spoke today of his expectations ahead of tomorrow's decision.
"What I expect the Supreme Court to do is to duck responsibility and bump it up to Europe (Court of Justice of the European Union) or maybe find against us but give us leave to appeal to Europe.
"The British courts have said right from the start they are not sure, but if it goes to Europe I expect the European courts to find in our favour."
Mr Rukin said such an outcome would set HS2 back four years, as it would have to 'start all over again', looking at alternatives it did not consider at the outset, such as other rail solutions or road.
"Right from the start this has been a test case, testing how (European environmental law) fits into UK law, and the European courts will almost certainly rule in our favour."
He said going to Europe would not be a victory in itself as it would not delay the progress of HS2 any further: the Government would simply plough on with the timetable while awaiting a ruling from Luxembourg, meanwhile 'wasting more taxpayers' money'.
But he believed it was already sufficiently held up – on what was an overambitious timetable in the first place – to become law before the country goes to the polls in spring 2015.
"There is no way way the hybrid bill can get through before the next general election, which makes HS2 an election issue," said Mr Rukin.
"The parties will have to decide where they stand on it."