IAN Blackford has hit out at Boris Johnson's "breathtaking arrogance" in not sacking Dominic Cummings for breaking lockdown rules.

The PM told the daily Downing Street briefing that his top aide "acted responsibly, legally and with integrity" in 250 miles between London and Durham despite the guidelines on travelling during lockdown.

READ MORE: PM says Dominic Cummings 'acted responsibly' in breaking lockdown

Blackford, the SNP's Westminster leader, said Johnson is "trying to take the public for fools".

He added: "Boris Johnson's breathtaking arrogance sends out the message that there is one rule for the Tory Government and another for the rest of us. He is trying to take the public for fools, but I have no doubt that people will see right through it.

“Families across all parts of the country have struggled through lock down, without the ability to call on friends and family for childcare. In a desperate attempt to save his adviser Boris Johnson has thrown public health advice and the solidarity and sacrifice of millions to the wind.

"The Prime Minister's refusal to act demeans his office and will cause lasting damage to public confidence in the Tory government and its response to Covid-19.

READ MORE: Nicola Sturgeon says Dominic Cummings must go after lockdown breach

"There is no question that Dominic Cummings broke the rules the minute he chose to drive to Durham. He is fatally undermining the public health message and must go.

"And the Prime Minister failed to answer a single question about what he knew, when, and where Mr Cummings was.

"Polling shows the majority of the public want Mr Cummings to go. With every hour the Prime Minister allows this farce to continue - the Tory Government loses more credibility and respect."

On Saturday, Mr Blackford called on the head of the civil service Sir Mark Sedwill to investigate the issue.

Earlier, Sturgeon tweeted: “I know it is tough to lose a trusted adviser at the height of crisis, but when it’s a choice of that or integrity of vital public health advice, the latter must come first.”

Referencing Dr Catherine Calderwood standing down from her post as Scotland’s chief medical officer after twice travelling from Edinburgh to her holiday home in Fife, she added: “That’s the judgment I and, to her credit, Catherine Calderwood reached. PM and Cummings should do likewise.”

When the comparison with Dr Calderwood’s situation was put to him and he was asked if Cummings’ actions would undermine the public health message, Johnson told the briefing: “No, because the sharp distinction is that unlike the lady who you mentioned, Mr Cummings actually went into lockdown, because he had symptoms, went into self-isolation for 14 days or more and that is what you should do.

“The particular circumstances of his isolation, as I’ve said now several times, were determined by the childcare needs of the family.”

Following the briefing, Sturgeon tweeted the Prime Minister’s comments about lockdown changes such as schools reopening do not apply in Scotland.

She added: “We are making progress against this virus but to avoid a resurgence we must move carefully. And we must maintain trust in public health advice.”