Downing Street said Johnson aide Dominic Cummings "believes he behaved reasonably and legally" when he travelled 400 kilometres during lockdown to visit family.
The UK's top government aide is facing new allegations he violated coronavirus lockdown rules by travelling 400 kilometres to northern England while his wife showed COVID-19 symptoms.
Members of the UK's opposition called for his resignation after it was firstly reported on Friday he violated the government's own coronavirus restrictions.
The Guardian and Mirror newspapers originally reported that Cummings travelled from London to his parents' house in Durham at the end of March during a nationwide lockdown.
Durham is located in north-east England more than 400 kilometres from London and under the lockdown that began March 23, the government had recommended avoiding non-essential travel and self-isolating in case of suspected COVID-19.
Cummings told reporters on Saturday he had "done the right thing" by travelling with his wife and son to be near family when she developed coronavirus symptoms at the end of March.
But the new reports cited witnesses who said they saw the government aide on 12 April in Bernard Castle, near Durham.
Two days later he was spotted in London and was then, according to the fresh reports, seen in Houghall Woods near Durham on 19 April.
Cummings has not responded to the new reports.
Downing Street said Saturday that Cummings made the first reported trip because his wife had coronavirus symptoms and he was likely to also get sick.
"It was essential for Dominic Cummings to ensure his young child could be properly cared for," a No 10 spokesperson said in a statement.
The PM's office said Cummings stayed in a house “near to but separate from” his extended family, adding that Cummings "believes he behaved reasonably and legally".
Transport secretary Grant Shapps said officials were "aware that not all measures would be possible" depending on circumstances, explaining that a child's welfare was important.
"We have always said in the guidance...we don't want to cause harm through advice that keeps people at home when they are at risk," said Dr Jenny Harries, England's deputy chief medical officer.
She said the advice was meant to keep people out of circulation and said there all of the guidance had a "common sense element" to it.
But on Sunday, other ministers from the ruling Conservative party said Cummings should resign.
Brexit campaigner and Conservative MP Steve Baker told Sky News: “I just see this rattling on now for day after day, wasting the public’s time, consuming political capital and diverting from the real issues we need to deal with... No-one is indispensable.”
Calls to resign
Opposition parties condemned Cummings' actions after the first reports of his alleged lockdown breach emerged on Friday
A spokesman for Labour, Britain's main opposition party, said "the British people do not expect there to be one law for themselves and another for Dominic Cummings".
Ed Davey, leader of the Liberal Democrats, said Cummings "will have to resign" if the facts are confirmed.
The Scottish National Party's leader in the House of Commons Ian Blackford said Cummings "must resign or be fired".
Cabinet minister Michael Gove took to Twitter to defend Cummings after Downing Street released the statement that explained the aide's actions.
"Caring for your wife and child is not a crime," Gove tweeted.
Cummings, 48, was one of the key architects of the Leave campaign of the EU referendum in 2016, which resulted in Britain leaving the European Union in January 2020.
He was appointed as one of the government's top aides after Boris Johnson won the 2019 general election.
_This article was updated to add new reports. _