But this morning Mr Johnson said the claims he lied to the Queen were "absolutely not" true.
Former attorney general Dominic Grieve warned that if ministers had misled the Queen over the reasons for prorogation, Mr Johnson's position would be untenable and he would have to resign.
He told the BBC: "Many people are saying - I'm not saying this - but, many people. are saying that the judges are biased".
The Court of Sessions in Edinburgh ruled on a case brought by 78 MPs after Mr Johnson first announced the suspension, which began on Tuesday.Judges said the PM was "motivated by the improper objective of stymying parliament".
I am not above it, no-one is above it - least of all Boris Johnson.
Meanwhile, the leader of the Scottish National Party (S.N.P.), Ian Blackford, has written to Prime Minister Johnson demanding that he recall parliament in light of the ruling in Scotland.
The Guardian says that, even if the Scottish decision is overruled on appeal next week, "the dishonesty of Mr Johnson's prorogation gambit has been recorded as a matter of fact".
"The UK government needs to bring forward a strong domestic legislative agenda".
It took leading judges nearly a week to return their reasons for rejecting the case brought by businesswoman Gina Miller about the prorogation of parliament.
They added: "The prime minister's decision that parliament should be prorogued at the time and for the duration chosen and the advice given to Her Majesty to do so in the present case were political".
It comes after three judges at Scotland's highest court in Edinburgh, ruled on Wednesday morning that the prorogation of parliament on Monday night by Johnson was unconstitutional.
The judges said the decision to prorogue and the advice given to the Queen were "inherently political in nature" and that there were "no legal standards against which to judge their legitimacy".
"The court agreed it is unlawful to suspend the UK Parliament for the specific goal of preventing Parliament from scrutinising the Brexit process and holding this shambolic Tory Government's extreme Brexit plans to account", she said.
MORE: Legal bid could empower Scottish court to extend Article 50 on Boris Johnson's behalf The case, brought by Ecotricity entrepreneur Dale Vince with Joanna Cherry QC MP and Jolyon Maugham, follows the anti-no deal Benn Act which legally obliges the government to either secure a deal with the European Union by October 19 or request an extension.
Mr Vince said this would "prevent a no-deal exit on October 31 and make the prime minister abide by the letter of the law, which he's suggested time and time against he's prepared to ignore".
Liberal Democrat Brexit spokesman Tom Brake warned ministers could not ignore the implications of the ruling.
It is the same team that brought the successful case which declared the prorogation of parliament unlawful.
With less than 50 days until the United Kingdom is due to leave, the government and parliament are locked in conflict over the future of Brexit, with possible outcomes ranging from leaving without a deal to another referendum.