The SNP has demanded a Cabinet Office inquiry into the Dominic Cummings scandal which saw the prime minister's top adviser travel 260 miles at the height of lockdown.
Ian Blackford, the party's Westminster leader, said the Tory aide must not be "completely unaccountable" for his alleged rule-breaking.
It comes as one former MP warns the row has "landed very badly" in Scotland and could dent support for the Union.
Cummings sparked fury throughout the nation after it was revealed he made 260-mile lockdown trips to Durham before later refusing to apologise.
He also claimed a journey to Barnard Castle was to 'test his eyesight' and make sure he was fit enough to drive back to London for work.
In a letter to the Cabinet Secretary ahead of the UK Parliament returning tomorrow, Blackford said the confirmation by Durham Police that there was a breach of the regulations - added to what Cummings already admitted wider breaches of the UK government guidance - meant there was a clear need for an inquiry.
"Dominic Cummings must not be left completely unaccountable for his actions," he said.
"No matter how exceptional he thinks he is - there cannot be one rule for Tory advisers and another for everyone else.
"There is a real sense of indignation that Boris Johnson has refused to take his responsibilities as Prime Minister seriously and failed to remove Mr Cummings from post - severely undermining trust in the UK government and its public health guidance."
Meanwhile, Stephen Kerr - who lost his Stirling seat to the SNP at last year's general election - said the future of the Union between Scotland and England now hung in the balance.
"There is no doubt that the whole Cummings saga has landed very badly in Scotland," he told The Times. "The SNP winning an ourtight majority at the next election is gong to introduce a whole range of stresses and strains on the Union.
"The next election will be about a bigger set of issues than Dominic Cummings - it will be about the future of Scotland, the record of the SNP over the last 12 years, jobs and the economy.
"What the Conservatives should be focusing on - and anyone who believes in the future of the Union - is what the Union has meant for our resistance to Covid, with the billions that have come to business supoort and the job retention scheme."
