Reports of the decision by Boris Johnson’s special adviser sparked calls for him to step down or be sacked.
However, the Great British Bake Off judge appeared to sympathise with Cummings when she quote-tweeted a post that read: “Dom and Mary’s journey was necessary and therefore within rules.
“What’s also necessary is not attacking a man and his family for decisions taken at a time of great stress and worry, the fear of death and concern for a child," the post continued.
“This isn’t a story for the normal political sh**kickery.”
Leith added her own comment: “Well said, Danny. How about a bit of kindness and tolerance?”
Grant Shapps, the transport secretary, appeared on the Sophy Ridge on Sunday Show as he attempted to dodge questions about Cummings.
“You'll probably remember, the prime minister during exactly the same period was pretty ill and, in fact, eventually in hospital in ICU, so I don't think this would have been high on the prime minister's agenda,” he said.
He categorically denied that Cummings went back to Durham after returning to London in mid-April, but failed to rule out reports that he made a sightseeing trip 30 miles from his family home on Easter Sunday.
Celebrities including JK Rowling and Charlie Brooker are among those to back the calls, with the Harry Potter author branding Cummings a hypocrite.