BORIS Johnson will learn tomorrow whether he could be fined or even jailed if he fails to seek an extension to avoid leaving the European Union without a deal.

Court of Session judge Lord Pentland is scheduled to rule on the action brought by SNP MP Joanna Cherry QC, Jolyon Maugham QC and businessman Vince Dale which asks the court to require the Prime Minister to apply for the extension and to allow the court to do so if he fails to.

Johnson's lawyers told Scotland's highest civil court that he accepted he must send a letter requesting a delay to Brexit beyond the Halloween deadline if no deal is agreed with Parliament by October 19. But the PM later said the options facing the country were his proposed new Brexit deal or leaving without an agreement, "but no delay".

He has previously said "we will obey the law" but will also leave on October 31 in any circumstance, without specifying how he would achieve the apparently contradictory goals.

If the court decides in favour of the Cherry petition any breach of the law could be ruled as a contempt of court, with the maximum penalty in Scotland up to two years in prison. However, whatever the decision tomorrow, it is unlikely to be decisive with the losing side almost certain to appeal up to the Supreme Court, mirroring Cherry's previous successful legal action.

Discussions between the UK and European Union are not taking place this weekend as anticipated as Brussels dealt a crippling blow to Johnson's new Brexit proposals. The European Commission said EU member states had agreed the proposals, which are intended to replace the controversial Irish backstop, "do not provide a basis for concluding an agreement".

A spokesman said the UK would be given "another opportunity to present its proposals in detail" tomorrow. The PM's Europe adviser, David Frost, has been in Brussels for technical talks with officials.

However Johnson's proposals have won support from the likes of Margot James – who was one of the 21 Tory rebels expelled from the party last month – and Paul Scully of the European Research Group of Tory Eurosceptics.

James said she thought she and the other sacked rebels would be able to support the PM's proposals.

"If the Prime Minister can get EU and Irish agreement then I think that we would – we've all got reservations – but we would be prepared to compromise and vote for the deal. Our prime concern really is to avoid Britain leaving without a deal."

Scully said there was a "lot of sympathy" among members of the ERG to get the deal through the Commons, adding: "It does most of the things that Leavers asked of our Government to sort out."

But Labour's Lisa Nandy said: "The truth is we're further away from a deal than we were two months ago and I can't see this getting anywhere."

According to EU sources, senior UK ministers have reached out to the Hungarian Government for assurances it would veto any request for a delay – seen as one way the PM could comply with the law and deliver Brexit this month. Any extension to the Article 50 process – the mechanism by which the UK leaves the European Union – would have to be unanimously agreed by all 27 leaders.