The Supreme Court's ruling focussed upon three constitutional questions:
In respect of the first question, the Court acknowledged the political context, but stated that "the courts cannot shirk that responsibility merely on the grounds that the question raised in political in tone or context”. The Court decided that it did have authority to rule upon such issues, by considering the alternative: not to do so would undermine parliamentary sovereignty as it would allow the Government to potentially to enter into longer and additional prorogations "…for as long as it pleased.”
As regards the lawfulness of the suspension, the Supreme Court developed a test for assessing the legality of a prorogation: a prorogation shall be considered unlawful if it “has the effect of frustrating or preventing, without reasonable justification, the ability of parliament to carry out its constitutional functions.”
Although some information was submitted to the Court for reason behind the prorogation, it was limited and crucially the Court took the view that it did not justify the length of the suspension. As a result the Court stated “It is impossible for us to conclude, on the evidence which has been put before us, that there was any reason, let alone a good reason, to advise Her Majesty to prorogue parliament for five weeks". The focus on the length of the prorogation has surprised some commentators, given that the decision was expected to focus upon the reasons given. This point was contentious because although the Government claimed the prorogation was undertaken because the previous Parliamentary session had been unusually long, numerous statements were made by Conservative politicians which suggested a desire to avoid Parliament intervening to disrupt the Government's Brexit plans was behind the decision.
As regards the appropriate remedy, the Court reached the view that due to the unlawfulness, no valid prorogation had occurred. The corollary of this is that the Prime Minister does not exercise discretion as to when Parliament returns and therefore Parliament will reconvene at 11.30am on 25 September 2019.
The Prime Minister, Boris Johnson, expressed disappointment in the ruling but accepted the outcome. He also confirmed that it remains his intention to deliver Brexit on 31 October 2019. However his ability to do so is likely to be affected by Parliament reconvening.
Given the uncertainty (as to whether the UK will exit the European Union on 31 October 2019 and if so, upon which terms) it becomes all the more important for business and citizens in the UK to regularly visit the Government's Brexit webpage to obtain the latest official advice on how to prepare.