LONDON -- British Prime Minister Boris Johnson's top adviser, Dominic Cummings, insisted Saturday that he behaved "reasonably and legally" when he travelled more than 250 miles (400 kilometres) to his parents' house during a nationwide lockdown at a time when he suspected he had the coronavirus.

Opposition politicians called for an urgent explanation after The Guardian and Mirror newspapers reported that Cummings, who lives in London, was seen at the property in Durham, northeast England, in late March and early April. A lockdown that began March 23 stipulated that people should remain at their primary residence, leaving only for essential local errands and exercise, and not visit relatives. Anyone with symptoms was told to completely isolate themselves.

Durham Police said that officers went to a house on March 31 and "explained to the family the guidelines around self-isolation and reiterated the appropriate advice around essential travel." Police did not mention Cummings by name.

Johnson's office said in a statement that Cummings made the trip because his wife was showing coronavirus symptoms, he correctly thought he was likely to also get sick, and relatives had offered to help look after the couple's toddler son. It said Cummings stayed in a house "near to but separate from" his extended family.

Asked about the trip by reporters outside his house in London, Cummings said "I behaved reasonably and legally."

"It's a question of doing the right thing. It's not about what you guys think." said Cummings, who also berated the journalists for failing to keep 2 metres (6 1/2 feet) apart in line with social distancing rules.

Cummings, a contentious figure who has a spiky relationship with the media, was one of the architects of the successful campaign to take Britain out of the European Union, and later was appointed Johnson's top aide.

Cumming's wife Mary Wakefield, an editor at news magazine The Spectator, wrote a vivid account last month of how they both were laid low with the virus, though she did not mention their travel in the article.

Cummings is one of a slew of senior British government figures to contract COVID-19, including the prime minister, who spent three nights in intensive care at a London hospital.

More than 36,000 people with the virus have died in the U.K., the second-highest confirmed total in the world after the United States.

Cummings, 48, is one of several senior U.K. officials who have been accused of flouting the lockdown rules that they advocated for the rest of the country.

Epidemiologist Neil Ferguson stepped down as government scientific adviser earlier this month after a newspaper disclosed that his girlfriend had crossed London to stay with him during the lockdown. In April, Catherine Calderwood resigned as Scotland's chief medical officer after twice travelling from Edinburgh to her second home.

Several senior government ministers defended Cummings's actions. Cabinet Office Minister Michael Gove tweeted: "Caring for your wife and child is not a crime." Health Secretary Matt Hancock, who was sick for a week with the coronavirus, said "it was entirely right for Dom Cummings to find childcare for his toddler, when both he and his wife were getting ill."

But critics of the government expressed outrage that Cummings had broken stringent rules that for two months have prevented Britons from visiting elderly relatives, comforting dying friends or even attending the funerals of loved ones.

Dave Penman, the leader of civil servants union the FDA, said "the prime minister needs to understand how heartbreaking this lockdown has been for so many families and the sacrifices that have been made up and down the country."

He said Johnson must explain why "it looks like there is one rule for those at the centre of government and one rule for rest of the country."