But a motion was filed at the Court of Session in Edinburgh by a cross-party group of more than 70 MPs and peers in a bid to stall Johnson.
“The legal action at one level is unusual as it seeks the court to intervene in a political decision,” he said.
“To take this action, they are using the fairly standard legal process of judicial review – which can only be heard in Scotland in the Court of Session.
“This procedure is generally used for decision-making in its broadest sense, not matters of policy.
“The difference here is that those raising the case, which includes MPs and Lords, is that they argue the decision fundamentally breaches the rule of law – which is seen as central to the UK Constitution.”
McKerrell explained it would be a “big ask” for the court to say the Queen, acting on the advice of the Prime Minister, is ignoring the UK constitution.
He said: “It is argued that the period of five weeks is far too extensive for prorogation as it overlaps with the period that Parliament can meet to consider the issues surrounding the withdrawal of the EU prior to exit day, as they call it, on October 31.
“This essentially will not leave enough time for democracy to properly function, thus the argument goes that the Court has to take action to make sure that the constitution is upheld.”
He added: “The fact that this is an action against an order the Queen herself has made would not stop the court ruling on it automatically.
“However, it would be a big ask for the court to say that the Queen acting on the advice of the Prime Minister and senior politicians is fundamentally breaking the rule of law and ignoring the UK constitution.
“We really would be in unprecedented territory there if that happened.”
Scottish court ruling on Brexit could put UK in ‘unprecedented territory’ – The National