"We have uncovered more and more evidence that this was a plot by Boris Johnson and his cronies to prevent us from stopping them taking Scotland and the United Kingdom off a Brexit cliff edge by forcing through a damaging no deal against the will of parliament".
"This is a valid ruling today by the court", Paul Sweeney, one of the politicians who had put their name to the legal challenge, told Al Jazeera.
They said they were unanimous in their belief that Boris Johnson had been motivated by the "improper objective of stymying Parliament".
A group of about 70 opposition lawmakers challenged the government's decision to prorogue, or formally shut down, Parliament, for five weeks until October 14 - just over two weeks before Britain is due to leave the EU.
MPs have demanded the immediate recall of Parliament following a landmark ruling by Scotland's highest civil court.
"The Supreme Court will now rule on the matter on Tuesday and the government will abide by that decision", said a government spokesperson.
The government immediately appealed, with the case set to be heard in the Supreme Court next Tuesday, and parliament set to remain shut in the meantime.
The British government will appeal against the Scottish appeal court's decision, which also contradicts a decision in Johnson's favour by senior English judges last week, at the supreme court. The UK Government needs to bring forward a strong domestic legislative agenda.
Jolyon Maugham, a lawyer who is part of the claim, said: "We believe that the effect of the decision is that Parliament is no longer prorogued".
Mr Johnson has previously insisted that it was normal practice for a new government to prorogue Parliament, and that it was "nonsense" to suggest he was attempting to undermine democracy.
Scotland's first minister, Scottish National Party (SNP) leader Nicola Sturgeon, echoed his call.
Speaking to Euronews, prominent Remainer and Labour peer Lord Adonis said: "Boris has time to waffle away on the internet but he refuses to speak to Parliament".
The judges added that the court "will accordingly make an order declaring that the prime minister's advice to HM the Queen and the prorogation which followed thereon was unlawful and is thus null and of no effect".
The petitioners to the Scottish Court of Session case included 13 Welsh MPs, including Geraint Davies, Lord Hain, Tonia Antoniazzi, Wayne David, Stephen Doughty, Jonathan Edwards, Ruth Jones, Ben Lake, Anna McMorrin, Madeline Moon, Owen Smith and Jo Stevens.
Shadow Brexit secretary Sir Keir Starmer speaking to the media.
A full hearing is scheduled at the Supreme Court on September 17.
"I urge the prime minister to immediately recall parliament so we can debate this judgement and decide what happens next".
Already, Downing Street is seeking to hit back politically, with a source quoted as saying that "legal activists choose the Scottish courts for a reason".
If Boris Johnson is found to have deceived the Queen he should quit, a former Tory MP has said.