A decision is expected to be made on whether the Prime Minister can be forced by the courts to send a letter requesting an Article 50 extension.
Documents submitted to the Court of Session on behalf of Boris Johnson were read out on Friday, in which he makes it clear he will not attempt to frustrate the so-called Benn Act.
However, the petitioners believe Number 10 cannot be trusted to abide by the law, so have launched legal action.
The legislation, passed by Westminster last month, requires the Prime Minister to ask the EU for a Brexit extension to January 31 if Parliament does not agree to any withdrawal deal Number 10 may come back with by October 19.
Legal action – led by businessman Vince Dale, SNP MP Joanna Cherry QC and Jolyon Maugham QC – was launched at the Outer House of the court.
It seeks to create an order which would force Mr Johnson to send the letter and prohibits him from frustrating the Act’s purpose.
This includes banning him from asking EU member states to deny the letter’s request or by sending an additional letter which contradicts it.
Aidan O’Neill QC, representing the campaigners behind the legal action, claimed Mr Johnson’s previous statements go against what he has said to the court through the documents.
He referred to promises made by the Prime Minister that he would rather be “dead in a ditch” than send a letter requesting an extension, and that the UK will leave on October 31 “do or die”.
Judge Lord Pentland is expected to announce his decision on the case on Monday.