The PM’s top aide made a public statement on Monday, where he extensively laid out what happened during his trip to Durham in March.
Mr Cummings said he made the journey to the North East because he was worried he and his wife may not be able to look after their child if they both fell ill.
Speaking after growing calls for him to resign, Mr Cummings said that by April 11 he had sought medical advice and was told it was safe to return to work.
However an intense backlash continues to rage with the Labour Party saying: “It’s one rule for Boris Johnson’s closest adviser, another for everybody else.”
But at the daily Downing Street press conference on Monday, the Prime Minister continued to show support for his key adviser.
He said: “Do I regret what has happened? Yes, of course I do regret the confusion and the anger and the pain that people feel.”
He added: “This is a country that has been going through the most tremendous difficulties and suffering in the course of the last 10 weeks and that’s why I really did want people to understand exactly what had happened.”
The Prime Minister said he had been told about Mr Cummings’ decision to drive to Durham to isolate while he was himself ill and “had a lot on my plate”.
“I didn’t know about any of the arrangements in advance,” Boris Johnson told the Downing Street press conference.
“What I think did happen was while I was ill and about to get a lot sicker we had a brief conversation in which I think Dominic Cuimmings mentioned where he was.
“But I have to tell you, at that particular stage I had a lot on my plate and really didn’t focus on the matter until these stories started to emerge in the last few days.”
When asked if he was prepared to revisit his decision to support Dominic Cummings, Mr Johnson said that he could not give anyone “unconditional backing”.
But he stressed that he did not believe that his any of his staff in Downing Street had done anything to undermine the lockdown messaging.
He added: “I cannot give unconditional backing to anybody, but I do not believe anybody in Number 10 has done anything to undermine our messaging.”
Boris Johnson said his own eyesight had been affected by coronavirus as he faced questions about why aide Dominic Cummings went for a drive to test his own vision.
The Prime Minister told the Downing Street press conference: “I’m finding that I have to wear spectacles for the first time in years – I think because of the effects of this thing – so I’m inclined to think there’s some … I think that’s very, very plausible that eyesight can be a problem associated with coronavirus.”
It follows Mr Johnson’s defence of Mr Cummings on Sunday, when said he could “not mark down” Mr Cummings for the way he acted.
The PM told Sunday’s Downing Street press conference that, following “extensive” talks with his aide, he concluded “he followed the instincts of every father and every parent”.
He said Mr Cummings had “acted responsibly, legally and with integrity”.