Dominic Cummings has broken his silence after it emerged he apparently flouted lockdown rules by travelling to Durham with his sick wife and child.
"I behaved reasonably and legally," he told reporters.
He added: “Who cares about good looks. It’s a question of doing the right thing. It’s not about what you guys think.”
No 10 have said the visit he made to Durham was “essential”.
In the first official comment since it emerged that the prime minister’s chief adviser had apparently flouted lockdown rules, Downing Street said his actions were “in line” with the guidelines.
Defending Mr Cummings, a No 10 spokesman said: “Owing to his wife being infected with suspected Coronavirus and the high likelihood that he would himself become unwell, it was essential for Dominic Cummings to ensure his young child could be properly cared for. His sister and nieces had volunteered to help so he went to a house near to but separate from his extended family in case their help was needed. His sister shopped for the family and left everything outside. At no stage was he or his family spoken to by the police about this matter, as is being reported. His actions were in line with coronavirus guidelines. Mr Cummings believes he behaved reasonably and legally.”
Members of the cabinet also defended Mr Cummings.
Rishi Sunak, the chancellor, tweeted: “Taking care of your wife and young child is justifiable and reasonable, trying to score political points over it isn’t.”
Dominic Raab, the foreign secretary, wrote in a similar vein: “It’s reasonable and fair to ask for an explanation on this. And it has been provided: two parents with Coronavirus, were anxiously taking care of their young child. Those now seeking to politicise it should take a long hard look in the mirror.”
Michael Gove, the cabinet office minister, added: “Caring for your wife and child is not a crime.”
Opposition politicians have accused No 10 of a ‘cover up’ after reports some in Downing Street knew Mr Cummings had made the 260-mile journey during lockdown.
Labour have called on Boris Johnson to say whether or not he sanctioned the trip.
SNP Westminster leader Ian Blackford said that Mr Johnson had questions to answer and should fire his chief adviser immediately.
Police have confirmed they visited a property in County Durham after Mr Cummings made the trip from his London home.
Following reports Mr Cummings and his wife travelled to his parents' home to get help to care for their young son, Mr Blackford told BBC Radio 4’s Today programme: “What I find interesting...is that (according to some reports) members of Downing Street knew about this so, first and foremost, Boris Johnson has serious questions to answer over what now appears to be a cover-up.”
Dave Penman, the general secretary of the FDA union, which represents senior civil servants, warned the “integrity of the prime minister” was at stake.
He called on Mr Johnson to state publicly if he believed Mr Cummings had adhered to the rules.
“It’s clearly a matter of public interest - lockdown has been heartbreaking for so many families, this looks like one rule for those at the centre of government and one rule for everyone else,” he said.
The details of Mr Cumming’s trip were revealed by the Daily Mirror and the Guardian.
A neighbour told the papers Mr Cummings was seen in the garden, while Abba's Dancing Queen was playing loudly.
Durham police confirmed officers had spoken to the owners of an address after reports a person had travelled there from London.
A spokesman said: "On Tuesday, March 31, our officers were made aware of reports that an individual had travelled from London to Durham and was present at an address in the city.
"Officers made contact with the owners of that address who confirmed that the individual in question was present and was self-isolating in part of the house.
"In line with national policing guidance, officers explained to the family the arrangements around self-isolation guidelines and reiterated the appropriate advice around essential travel."
Senior members of Mr Johnson’s own party expressed concern Mr Cumming’s journey could endanger the government’s plans to lift the lockdown.
Former Tory cabinet minister David Lidington, Theresa May’s de facto deputy prime minister, told Newsnight: "There's clearly serious questions that No 10 are going to have to address, not least because the readiness of members of the public to follow government guidance more generally is going to be affected by this sort of story."
Professor Neil Ferguson, the epidemiologist whose modelling prompted the lockdown, quit as a government adviser for flouting the rules when he was visited at this home by his girlfriend.
At the time Matt Hancock, the health secretary, said he was "speechless" and said he backed any police action against Mr Ferguson.
Sir Ed Davey, acting leader of the Liberal Democrats, called for Mr Cummings to quit over the allegations, while a spokesman for Labour said: "The British people do not expect there to be one rule for them and another rule for Dominic Cummings."
He told the BBC Mr Johnson had serious questions to answer. “Did he sanction this? Did he say “this is ok”?”
Allies of Mr Cummings said he was not “remotely bothered” by the story, calling it “fake news”.
"There is zero chance of him resigning."