BORIS Johnson has been accused of displaying “breathtaking arrogance” after he defied widespread calls, including from Conservative MPs, to sack Dominic Cummings and, instead, announced he was sticking by his chief adviser.

The Prime Minister was forced to lead the daily Downing St briefing as the furore over Mr Cummings’s 250-mile trip from London to Durham during the lockdown sparked a wave of anger and indignation.

But, instead of complying with calls for his de facto chief of staff to go, including one from Nicola Sturgeon, Mr Johnson declared that Mr Cummings had "acted responsibly, legally and with integrity" in seeking to look after his four-year-old son.

“I have had extensive face-to-face conversations with Dominic Cummings and I have concluded that in travelling to find the right kind of childcare - at the moment when both he and his wife were about to be incapacitated by coronavirus and when he had no alternative - he followed the instincts of every father and every parent and I do not mark him down for that," insisted the PM.

He went on: "Though there have been many other allegations about what happened when he was in self-isolation and thereafter, some of them palpably false.

“In every respect he has acted responsibly and legally and with integrity and with the overwhelming aim of stopping the spread of the virus and saving lives."

While the Government has strongly denied a claim Mr Cummings made a second trip to Durham after recovering and returning to London, Mr Johnson conspicuously failed to answer a question about another claim that during his lockdown his chief aide made a trip to Barnard Castle 30 miles away on Easter Sunday.

Reports suggested the No 10 aide could face a police investigation for a possible legal breach of the self-isolation rules over this alleged trip away from Durham.

On Wednesday, the PM is set to be grilled over the Cummings affair when he appears before senior MPs on the Commons Liaison Committee.

Last night, there was a wave of denunciation from party political opponents and others following the press conference.

In an astonishing development, a tweet from the official UK Civil Service Twitter account read: "Arrogant and offensive. Can you imagine having to work with these truth-twisters?"

It was later taken down. A UK Government spokesman said the tweet was “unauthorised” and an investigation had been launched into the matter.

At Westminster, Sir Keir Starmer declared: “This was a test of the Prime Minister and he has failed it.

“It is an insult to sacrifices made by the British people that Boris Johnson has chosen to take no action against Dominic Cummings. The public will be forgiven for thinking there is one rule for the Prime Minister’s closest adviser and another for the British people.”

The Labour leader added: “The Prime Minister’s actions have undermined confidence in his own public health message at this crucial time. Millions were watching for answers and they got nothing. That’s why the Cabinet Secretary must now launch an urgent inquiry.”

Ian Blackford, the SNP leader in the Commons, described Mr Johnson’s performance at the press briefing as “excruciating”.

He said: “Boris Johnson's breathtaking arrogance sends out the message 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 lockdown 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,” added the Skye MP.

Sir Ed Davey, the acting leader of the Liberal Democrats said: “Millions of people who’ve made huge sacrifices to keep to the rules will be astonished and angry at how the Prime Minister is now bending the rules for his closest aide.

“By failing to act, the PM undermines his own authority to lead the country through this appalling crisis, bringing his own judgement into question.”

Green MP Caroline Lucas said Mr Johnson’s press conference performance was “unbelievable”.

She tweeted: “PM says Cummings has acted 'responsibly, legally and with integrity'. In fact, he's acted arrogantly, illegally and with gross irresponsibility. Even by PM's own abysmal standards, this must surely be the lowest point."

Veteran Tory backbencher, Sir Roger Gale, who had been among several Conservative MPs calling for Mr Cummings to go, said he was "very disappointed" with the PM's decision to defend him.

“It was an opportunity to put this to bed and I fear that now the story is simply going to run and run," he noted.

Paul Maynard, the former Conservative minister, issued a withering response, saying: “I can only share the collective dismay and I understand the widespread anger.”

In Scotland, the SNP’s Joanna Cherry took to social media, tweeting: “We are living in a state run by an unelected political adviser who has made the PM his puppet & operates above the law. Really. Quite. Frightening.”

Her fellow Edinburgh MP, Labour’s Ian Murray posted: “I knew Theresa May wouldn’t hold the crown of the worst PM in history for very long. That press conference was embarrassing. The PM has just lied on national television. The message of ‘he used his instincts’ is not the instructions. No credibility left.”

Jackson Carlaw, the Scottish Conservative leader, conspicuously failed to say if Mr Johnson had done the right thing by sticking by Mr Cummings but simply said: “I've heard what the Prime Minister has said and it is a situation for him to judge. He has reached a conclusion and we must all now focus on continuing to beat this dreadful pandemic.”

Ms Sturgeon tweeted a response, saying: “Strangely different to his view on Cath Calderwood. Leadership is saying/doing the right thing even when it’s tough for you - not just calling for it when it’s tough for your opponent.”

At the press conference, Mr Johnson – who announced the daily UK death toll had risen by 118 to 36,793 – said the Government was now ready to move to “step two” of its strategy to ease the lockdown, which would involve the phased reopening of schools in England from June 1.

“In line with the approach being taken by other countries, we want to start getting our children back in the classroom in a way that is manageable and as safe as possible,” he explained.

However, some parents, teachers, unions and local authorities are opposed to the idea.

The FM tweeted a reminder, saying the PM's “comments just now on lockdown/schools applies to England” and in Scotland “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".

Mr Johnson pointed out how the Government’s assessment of making other changes, such as the reopening of non-essential shops, would be made public “in detail in the coming days”.

Today, the PM will chair a meeting of the Cabinet, which will discuss “step two” measures but which could also touch on the political furore over Mr Cummings.