“Shocking and disgraceful” attacks on the integrity of the Scottish judges who ruled the decision to prorogue Parliament was unlawful are “deeply dangerous”, Nicola Sturgeon said.

The Scottish First Minister spoke out after Downing Street was forced to distance itself from claims that the three judges at the Court of Session in Edinburgh were “politically biased”.

Sources in No 10 were reported as having suggested that the MPs and peers who brought the legal challenge “chose the Scottish courts for a reason”.

The Prime Minister’s official spokesman later made clear that “we absolutely respect the independence of the judiciary”.

But Ms Sturgeon said: “What we heard directly and indirectly from key people within the Conservative Party attacking the independence and integrity was absolutely disgraceful and shocking.”

She added: “Whatever our views on individual judgments, our court system is a vital part of our democracy and the separation of powers.

“It is not just wrong but deeply dangerous for politicians of any party to attack the independence of the judiciary.”

The First Minister spoke after three senior Scottish judges declared that Boris Johnson’s decision to suspend Parliament was both “improper” and “unlawful”.

The judges, chaired by Lord Carloway, Scotland’s most senior judge, concluded prorogation had been done with “the purpose of stymying Parliament”.

Judge Lord Carloway (David Cheskin/PA)

Speaking at First Minister’s Questions in the Scottish Parliament, Ms Sturgeon said the ruling – which will now be considered by the UK Supreme Court – was of “huge constitutional significance”.

And with the Yellowhammer paper on planning for a no-deal Brexit having been published, she stressed it was now vital for MPs to return to the House of Commons.

“It is vital that Parliament is there scrutinising and holding to account this Government,” she said.

“The big question for the Prime Minister and the Government this morning is why on earth Parliament is still suspended?

“We had Scotland’s highest civil court yesterday declaring the prorogation of Parliament as unlawful.

“Parliament should be back to work scrutinising this Government because if any government needed scrutinising, this UK Government certainly does.”