A Scottish judge has fast-tracked a legal challenge backed by 75 MPs and peers to prevent Boris Johnson proroguing parliament to force through a no-deal Brexit.

The cross-party group, led by the Scottish National party MP Joanna Cherry QC, alleges it would be illegal and unconstitutional for the prime minister to suspend the Commons to prevent MPs blocking a no-deal Brexit before 31 October.

They told Lord Doherty in the court of session “the petition raises legal issues of profound constitutional significance, and these require to be considered and determined as a matter of extreme urgency”.

Doherty ruled an urgent hearing of the case should take place on Friday 6 September, giving both sides only 10 days to prepare their legal arguments and four more days to revise them.

The case has been brought by a cross-party group of Labour, SNP, Liberal Democrat and former Tory MPs who quit the party over Brexit, and the Good Law Project, the anti-Brexit campaign group set up by Jolyon Maugham QC. Another two MPs are due to join the group before the next hearing.

Q&A What does 'prorogue parliament' mean? Show Prorogation is the official term that marks the end of a parliamentary session. After being advised to do so by the prime minister, the Queen formally prorogues parliament. This takes the form of an announcement in the House of Lords on the Queen’s behalf. It is a speech, written by the government, which usually describes the bills that have been passed during that session and summarises what has been achieved. It means that all work on existing legislation stops, and MPs and Lords stop sitting. Prorogation also automatically kills any bills, early day motions or questions to ministers going through parliament. Parliament can then be reopened a few days later with a fresh slate of legislation intentions, set out in a new Queen’s speech at the formal state opening of parliament.

It follows a historic victory for a cross-party group of Scottish parliamentarians and Maugham in the European court of justice last December, which said the UK was legally able to revoke article 50 without the EU’s approval.

In two minor victories for the UK government, Doherty refused the group’s plea for the case to be immediately sent to Scottish appeal judges to speed the process up, and also accepted the government’s compromise proposal for costs should be capped and shared between both sides.

David Welsh, the advocate acting for the parliamentarians and Maugham, told the court they feared the government would block and slow down the case as much as possible.

He said the applicants were running desperately short of time: in order for a final judgment on whether proroguing parliament was lawful before 31 October, the case needed to be heard by the ordinary court, the appeal court and finally the UK supreme court in only 11 weeks.

Welsh warned that legal delays in reaching a final decision meant Johnson could prorogue parliament before the case had ended. A no-deal Brexit would have “severe and irreversible” consequences. “It is a rather exceptional request against a highly exceptional and unusual background,” he added.

Andrew Webster QC, the government’s lawyer, denied that ministers wanted to obstruct the case and accused Welsh of “misreading and mischaracterising” the government’s view it would be wrong to immediately refer the case to the appeal court.

Webster told Doherty the UK government also wanted it heard and decided before the UK’s departure deadline. “The respondent is willing to seek to deal with these matters before 31 October provided that is done in a fair and proportionate manner,” he said.

He admitted this was a “challenging timetable” but said allowing the main case in the lower court to be heard in five weeks, gave the appeal court and supreme court six weeks to finally decide.

The case will hinge on whether Johnson would be breaching established constitutional law and both the EU Withdrawal Act 2018 and the Northern Ireland (Executive Formation etc) Act 2019 if he asked the Queen to prorogue parliament.

The petition argues the EU Withdrawal Act requires parliament to ratify the final Brexit deal and the Northern Ireland act was amended by Dominic Grieve, the former attorney general, to ensure parliament sat from September to December 2019, and heard fortnightly reports by ministers, to scrutinise the Brexit process.