Boris Johnson is facing a revolt from within his own party as MPs from across the political spectrum line up to condemn the prime minister and his chief adviser Dominic Cummings.

A storm of protest continues to rage not only over revelations the prime minister’s most senior and most trusted aide broke the Government’s own lockdown guidelines, but also due to Mr Johnson’s defence of Mr Cummings on Sunday.

Mr Cummings travelled to County Durham in March to self-isolate with his family while official guidelines warned against long-distance journeys, apparently because he feared that he and his wife would be left unable to care for their son. Further reports also suggested he took a second trip to the North East in April.

Mr Johnson fronted Downing Street’s coronavirus briefing to back Mr Cummings, saying he had “acted responsibly, legally and with integrity” and that “any parent would frankly understand what he did”.

Dissent has come from inside Tory party ranks, with former minister Paul Maynard saying he shared people’s “dismay” at the response, and was one of many MPs who insisted Mr Cummings should quit or be sacked.

“It is a classic case of ‘do as I say, not as I do’ – and it is not as if he was unfamiliar with guidance he himself helped draw up,” he said.

“It seems to me to be utterly indefensible and his position wholly untenable.”

Veteran Conservative Sir Roger Gale told the PA news agency: “I’m very disappointed, I think it was an opportunity to put this to bed and I fear that now the story is simply going to run and run.”

Senior Tory MP Simon Hoare, who had already called for Mr Cummings to go, later lamented Mr Johnson’s press conference, telling the Daily Mail: “The PM’s performance posed more questions than it answered. Any residual hope that this might die away in the next 24 hours is lost.”

Somerton and Frome MP David Warburton said Mr Cummings was “damaging the Government and the country that he’s supposed to be serving”.

Speaking on BBC Breakfast on Monday morning, he said his own father had died alone as a result of the coronavirus lockdown.

“People have made sacrifices, this is a difficult time, this is a time of national crisis,” he said.

“In those sacrifices there really hasn’t been the choice to use instinct.

“Instinct hasn’t really been part of it.

“We’ve been tasked with following regulations laid down by the Government.”

Tory grandee Lord Heseltine said it was “very difficult to believe there isn’t a substance” in the allegations about Mr Cumming’s movements.

“I think these unanswered questions are now on the agenda,” he told the BBC, “and I don’t think that this anxiety about the Government’s position will end until we know the whole story.”

Another Tory MP, Jason McCartney, said while it was important for people to show compassion during the crisis, Mr Cummings had to go because the “perceived hypocrisy of the rule makers potentially threatens the success of any future measures” under a second wave of the coronavirus.

“We must have confidence that we are doing the right things for the right reasons and that we are all truly in it together. For that reason I believe Mr Cummings’ position is now untenable,” Mr McCartney said in a Facebook post.

Drawing attention to “the moral hazard of Cummingsgate”, Tory MP George Freeman retweeted an article from The Spectator which said Mr Johnson’s judgement was “now the issue”.

In another tweet, Mr Freeman appeared to bemoan what was missing from the responses of the PM and his main adviser, saying: “Today we needed: some humility; a clear acknowledgement that people would be rightly angry if they sensed double standards; a sincere thank you to the millions of people (including fathers) who have made sacrifices Dominic Cummings didn’t; and a public apology from him”.

Labour leader Sir Keir Starmer tweeted Mr Johnson had failed a test of leadership, saying his decision to take no action against Mr Cummings was “an insult to sacrifices made by the British people”.

Labour MP Paul Blomfield echoed his leader, saying Mr Johnson had “treated the British people with contempt”.

And Labour’s shadow health minister Justin Madders said it appeared Mr Johnson was now alone in supporting Mr Cummings, saying the matter was “now a question of the PM’s judgment and leadership”.

Scottish First Minister and SNP leader Nicola Sturgeon said Mr Cummings should either resign or be sacked, pointing out she had had to accept the resignation of Scotland’s chief medical officer adviser Catherine Calderwood last month for her own lockdown breach.

“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,” Ms Sturgeon tweeted.

“That’s the judgment I and, to her credit, Catherine Calderwood reached. PM and Cummings should do likewise.”

Acting Liberal Democrat leader Ed Davey tweeted “Cummings must go”, saying the public would be “confused and angry” that he is still in his position.

The LibDems’ Jamie Stone called the Cummings affair “a disgrace that stinks in the nostrils of all decent people”.

And LibDem peer Lord Rennard called for Mr Cummings’ sacking and for his full disclosure, citing Mr Cummings’ handling of last year’s sacking of Treasury media adviser Sonia Khan as a precedent.