British Prime Minister Boris Johnson's closest adviser, Dominic Cummings, travelled more than 400 kilometers from his London home after showing symptoms of coronavirus, breaking the government's lockdown rules, the Guardian and Mirror newspapers reported on Friday.

Cummings, a polarizing figure in Britain since he masterminded the successful campaign to leave the European Union in 2016, traveled to Durham in northern England in late March, when a strict lockdown was already in place, the reports said.

A spokesman for Johnson's Downing Street office said it would make no comment.

The opposition Labour Party said Downing Street should explain his actions. "The British people do not expect there to be one rule for them and another rule for Dominic Cummings," a spokeswoman said.

According to the two newspapers, Cummings, who had developed symptoms of the disease on the weekend of March 28-29, was at his parents' house in Durham on March 31. This was a week after the prime minister imposed a nationwide lockdown that banned non-essential travel.

"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," a spokesman for Durham police was quoted as saying in both newspapers' reports.

"Officers explained to the family the guidelines around self-isolation and reiterated the appropriate advice around essential travel."

The BBC quoted a source close to Cummings as saying he did travel to Durham during lockdown but did not breach the rules as he needed his parents' help with childcare while he was ill. Cummings and his wife have a young son.

Observers speculate that Cummings may have played a vital role in delaying Downing Street's coronavirus response and that he was also an enthusiastic advocate of "herd immunity," a response strategy that was banished due to its controversy.  

While Cummings is known for his defiance of conventional wisdom as well as his propensity to upset the established order, the reports could put Cummings in a difficult position, as several other senior officials who had reportedly broken the lockdown rules were forced to resign from their posts. 

Epidemiologist Neil Ferguson resigned from his role as a government adviser on May 5 after the Daily Telegraph reported he had met his girlfriend.

Scotland's Chief Medical Officer Catherine Calderwood resigned on April 5 after she broke her own advice to stay at home by visiting her second home on two weekends.

Ed Davey, acting leader of the Liberal Democrats, said that if Cummings had broken the rules, "he will have to resign."

(Cover image: Dominic Cummings, special adviser for Britain's Prime Minister Boris Johnson arrives in Downing Street, amid the COVID-19 outbreak, London, Britain, May 21, 2020. /Reuters)