From BBC:

13:30
PM considers Cummings issue closed - No 10
Boris Johnson is standing by his top aide Dominic Cummings, following the Durham Police findings.

A No 10 spokesman said: "The police have made clear they are taking no action against Mr Cummings over his self-isolation and that going to Durham did not breach the regulations.

"The prime minister has said he believes Mr Cummings behaved reasonably and legally given all the circumstances, and he regards this issue as closed."

and

Durham Constabulary said it views "this as minor because there was no apparent breach of social distancing" during the trip.

You have to leave your car to breach regulations? That wasn't made clear in the guidelines.

Also, as much as Boris Johnson believes this matter to be over, it is very far away from being over.