One of the key figures in the legal case against Boris Johnson's suspension of parliament has said she is "confident" the UK Supreme Court will rule against him.

SNP MP Joanna Cherry said it was "reasonably likely" the Supreme Court will agree with a stunning ruling in Scotland's highest civil court on Wednesday, which found the conduct of UK ministers "unlawful".

She was a petitioner in the successful Court of Session case, which saw three judges unanimously rule Johnson's five-week prorogation of parliament illegal.

It was a reversal of an earlier decision by the court, after Cherry and her fellow petitioners brought an appeal.

A cross-party group of around 75 MPs and peers was behind a case, with a near-identical case in England rejected by the High Court in London.

The Supreme Court is due to make a final ruling the issue at some point in the next few weeks.

Speaking to Scotland Tonight on Wednesday, the SNP MP highlighted internal government documents revealed during the Edinburgh case which showed Johnson had green-lit suspending parliament two weeks before it was made public.

Cherry said the papers "showed that Boris Johnson was not telling the truth".

She went on: "The court heard legal argument and could reach the deduction that there was an improper motive here.

"I am pretty confident that the Supreme Court will reach the same view.

"Look at it this way: if the Supreme Court finds that what's happened is alright, then the UK Supreme Court will have said that under the British constitution, it is possible for the British minister to prorogue parliament for any reason and for as long as he likes.

"In a situation when he is running a minority government, and he doesn't want parliament to scrutinise what he's up to.

"If that is British democracy then it is not up to much."

Given the Court of Session ruling, Cherry also called on MPs to return to the House of Commons, although the Government does not have to recall parliament unless the Supreme Court also rules against it.

The SNP MP told Scotland Tonight: "There is nothing in law to stop parliament resuming in the meantime.

"If the British government had wanted parliament to be prevented from resuming on the back of this decision, they should have moved for the decision to be suspended pending the outcome of the Supreme Court.

"They did not do that.

"Every day that parliament is not sitting is another day where Boris Johnson can get up to mischief, without any parliamentary scrutiny."

She went on: "Even if the Supreme Court does find in our favour, which I think is reasonably likely, they won't do so until the week after next and we will have lost about ten days of parliamentary time.

"That is not just the time in the House of Commons chamber, it is also time that all of these committees, these select committees, are sitting, taking evidence from experts and scrutinising the process of Brexit."