LONDON — British Prime Minister Boris Johnson came under pressure Saturday to dismiss his top aide, the strategist and sloganeer Dominic Cummings, who may have violated strict quarantine rules by taking a 260-mile family road trip while he and his wife were infected with the coronavirus.

Cummings was the messaging mastermind behind Johnson’s successful 2016 Brexit campaign who coined the phrase “take back control.” Later, he was the brains behind Johnson’s landslide victory in the December general election, winning with another Cummings coining, the promise to “get Brexit done.”

Now Cummings is on the griddle after the Guardian and Mirror newspapers revealed Friday that the special adviser traveled from London to his parents’ house in Durham in northern England in late March — just as Johnson began his difficult bout with covid-19.

At the time, a strict lockdown was in place and top government ministers were hammering away at the public with the punchy message to keep the National Health Service from being overwhelmed: “Stay at Home. Protect the NHS. Save Lives.”

Instead, Cummings, his wife, Mary Wakefield, an editor at the conservative magazine the Spectator, and their young son fled from the capital city to the countryside, even as the government was begging citizens not to travel to second homes, to stay indoors and, for those with symptoms, to follow strict quarantine measures to control the contagion.

Cummings has the British prime minister’s “full support,” said Grant Shapps, the transport secretary, at a news conference. Shapps said that Johnson knew that Cummings was unwell and was staying in one place, but he didn’t say whether Johnson was aware that his top aide had driven across the country.

Later, however, the Observer and Sunday Mirror reported that he further broke the lockdown rules with a second trip to Durham.

The Durham police also issued a statement, saying that an officer had spoken to Cummings’s father on April 1, who said that his son was at an address in Durham and “self-isolating in part of the property.”

Earlier on Saturday, Downing Street issued a statement about Cummings, saying that “at no stage was he or his family spoken to by the police about this matter, as is being reported.”

Cummings’s apparent flouting of the rules has sparked an angry cry for his head from opposition politicians and ordinary citizens who say that government officials are hypocrites who tell the public to do one thing while they do another.

Many in Britain have not seen their friends and relatives since the lockdown was announced March 23 — missing births, graduations, weddings and funerals. Sunbathers have been fined by police. Residents in the countryside have warned “corona-idiots” from the cities to stay away.

Opposition lawmakers said that if Cummings broke the guidelines, then he needs to go.

“It is as simple as that,” said Ed Davey, the acting leader of the Liberal Democrats.

Cummings is a larger-than-life maverick in British politics. His leading role in the 2016 Brexit campaign was portrayed by Benedict Cumberbatch in the HBO film “Brexit: The Uncivil War.” With his bald dome and his casual hoodies, the 48-year-old political fixer is better known than most of Johnson’s tailored ministers. He also wears a target on his back.

In late March, Cummings was filmed rushing out of Downing Street, shortly after Johnson tested positive for the coronavirus.

After 10 days of self-isolation at the official residence, the prime minister was so sick he was taken to the hospital and then to its intensive care unit, where he was given supplemental oxygen. Upon his release, Johnson said he was lucky to be alive.

Downing Street issued a statement on Saturday that Cummings did nothing wrong.

“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,” the statement said. “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.”

That would be the residence in Durham. “His actions were in line with coronavirus guidelines,” the statement read. “Mr. Cummings believes he behaved reasonably and legally.”

Asked by reporters camped outside his London home on Saturday if it looked good for a senior government adviser to ride out his symptoms far from home, Cummings replied: “Who cares about good looks? It’s a question of doing the right thing. It’s not about what you guys think.”

Officials around the world have been caught flouting the same lockdown rules they helped put in place. Britain is no exception.

Earlier this month, Neil Ferguson, an epidemiologist whose work has been pivotal in the British government’s response to the outbreak, quit his government advisory role after he was found to have breached lockdown rules to meet his married lover. Catherine Calderwood, Scotland’s chief medical officer, resigned from her post after she made two trips to her second home.

Fleet Street was poring over an article that Cummings’s wife published in the Spectator. She wrote about she and her husband falling ill — “he could breathe, but only in a limited, shallow way” — but she made no mention of trips to Durham.

Officials rallied around Cummings. Michael Gove, a senior member in the Conservative government, wrote, “Caring for your wife and child is not a crime.” Health Secretary Matt Hancock, who himself was stricken by the virus, tweeted: “I know how ill coronavirus makes you. It was entirely right for Dom Cummings to find child care for his toddler, when both he and his wife were getting ill.”

Critics said it was hypocritical for those in the government to push rules they themselves don’t obey.

Harry Potter author J.K. Rowling, reflecting the thoughts of many, wrote on social media: “One of the architects of the rules keeping those people housebound drove across the UK, knowing he had the virus. Indefensible hypocrisy and selfishness.”

A Durham resident who lives near the Cummings family home agreed, telling the Guardian: “It’s one rule for Dominic Cummings and one rule for the rest of us.”