British Prime Minister Boris Johnson’s closest aide defied calls to quit on Monday over accusations that he flouted a coronavirus lockdown by driving 250 miles from London to northern England.

In a statement which he read to media in the Rose Garden of Johnson’s 10 Downing Street office, Dominic Cummings said he believed he had acted reasonably and had not violated the lockdown rules.

“I did what I thought was the right thing to do,” Cummings said in response to reporters’ questions after delivering the statement, which he issued in an open neck shirt. “I think…I behaved reasonably”.

Johnson had defended Cummings on Sunday, saying the advisor acted “responsibly and legally and with integrity” when he travelled 400 km (25 miles) in March from London to County Durham in northern England with his son and wife, who had symptoms of COVID-19, to be with relatives.

Cummings, who fell ill himself after the long drive, explained that he had wanted to ensure his four-year-old son could be properly cared for if he fell ill.

At the time, strict lockdown rules were in place and Johnson’s intervention backfired, with a growing chorus of critics questioning his own judgment.

Some lawmakers, bishops, scientists, doctors and police officers said Cummings’ apparent disregard for the rules imposed on everyone else had undermined efforts to control the coronavirus outbreak.

Cummings, 48, could still face pressure to quit despite his statement, and his departure would be a big loss for Johnson.

Cummings, who expressed no regret over the journey, helped Johnson win power last year and was the architect behind the successful 2016 referendum campaign to secure Britain’s exit from the European Union.

With a death toll of around 43,000, Britain is the worst-hit country in Europe and the government had already been under pressure over its handling of the pandemic.

Reuters