The former Tory MP, who supported a bill to block Mr Johnson from carrying out a no deal Brexit, hit out at the Prime Minister following the ruling from the Scottish court. Mr Grieve has insisted Mr Johnson should resign if he is found to have misled the Queen over his reasoning for shutting down Parliament. His comments come in what will be seen as a major win for Remainers plotting to derail the Prime Minister’s Brexit Strategy.
Speaking to BBC News, Mr Grieve said: “When the Government says it’s doing something for a particular reason they must be able to sustain that.
“If it turns out they are doing it for another reason that is a breach of one of the fundamental tenets of how we operate and so it must be the case.
“The relationship between the Prime Minister and the sovereign is concerned it is one of complete and mutual confidentiality and Mr Johnson has a duty of total candour towards the Queen when asking her to discharge her functions.
“It’s essential otherwise our constitution can’t work.
“I think if that were to be the case, Boris Johnson would find himself in an untenable position in Parliament.
“I hope it will be untenable not just because of the opposition because every member of our Conservative party who believes in the constitution would simply say it’s over.”
The case against Mr Johnson was led by Lib Dem leader Jo Swinson and SNP MP Joanna Cherry.
Ms Cherry tweeted: “Huge thanks to all our supporters and our fantastic legal team who have achieved the historic ruling that #prorogation is #unlawful.”