The government, had a legal power to prorogue parliament, but it was litigated and the argument was that the government were acting in bad faith and the real intention was to suppress the role of parliament.
A government, facing a legal challenge of bad faith, needed to put down a witness statement from a minister or a senior civil servant explaining how the decision was made. That is what should have happened. For some reason, a witness statement was not put in in this Scottish case, and in the final judgement that has turned out to be crucial.
In the absence of an account by the government of why they took this decision to prorogue parliament it became open to the Scottish judges to infer, in the absence of a positive plausible explanation, that there was a bad motive, that it was being done to stop parliamentary scrutiny.
Unanimously, all three Scottish judges said that the failure of ministers to offer a convincing reason for suspending parliament led them to rule that the motivation was to avoid scrutiny and push through Brexit on October 31 with or without a deal. The only explanation for this prorogation is thus ‘improper motive’. And if it's improper motive, then it's unlawful.
So why wasn't a witness statement submitted by the government? That's where things get more interesting. The reason there wasn't a witness statement is because it seems that nobody would risk the legal peril of signing it. As it's a criminal offence to knowingly mislead a court, it would appear that something prevented somebody happily signing a witness statement explaining the true reason why prorogation was sought.
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Lord Brodie [senior Scottish judge] said the government used its powers “for an improper purpose and in an unreasonable manner” by preventing parliament from holding it to account in the run-up to leaving the EU.
He accused Mr Johnson of failing “to give a proper and complete account of the executive’s true reasons for exercising the prerogative to prorogue parliament”. He said the refusal meant “that the court should draw inferences of fact against the respondent”.
Lord Brodie added: “I would infer . . . that the principal reason for the advice to the Queen to make the order for the prorogation of parliament was to prevent or impede parliament holding the executive politically to account in the run-up to exit day; to prevent or impede parliament from legislating on the United Kingdom’s exit from the European Union; and to allow the executive to pursue a policy of no-deal Brexit without further parliamentary interference.”