Dominic Cummings has refused to quit after it was revealed that he had driven 400 km (250 miles) from London to northern England in March with his 4-year-old son and his wife, who was sick at the time, to be close to relatives.

Johnson has repeatedly backed his adviser.

"It's been a very, very frustrating episode and I understand why people ... have been so concerned, because this country is going through a horrendously difficult time," Johnson told a parliamentary committee on Wednesday (May 27).

Opinion polls show that faith in Johnson has tumbled since the Cummings story broke on Friday in The Mirror and The Guardian newspapers, with some people openly lampooning both the prime minister and his aide on social media.

Opposition parties and some Conservative lawmakers have also demanded that Cummings, the man behind the successful 2016 Brexit campaign and Johnson's landslide 2019 election victory, should resign.

He has refused to apologize.