Theresa May is the latest senior politician to speak out over Dominic Cummings and how he broke lockdown rules.
The former prime minister has accused the No. 10 aide of failing to "follow the spirit" of the currently guidance over the coronavirus crisis.
She also said that she could "well understand" the public's anger at Cummings' behaviour when he drove 260 miles from London to Durham.
The journey happened during April when people across the country were isolating away from their families and loved ones.
According to Mirror Online, May's comments are a fresh blow to Boris Johnson as the Tory civil war over Mr Cummings continued.
Delivering her verdict in a statement to her constituents in Maidenhead, Berks, Mrs May said: “What this matter has shown is that there was a discrepancy between the simple messages given by the Government and the details of the legislation passed by Parliament.
“In these circumstances I do not feel that Mr Cummings followed the spirit of the guidance.
“I can well understand the anger of those who have been abiding by the spirit of the guidance given by the Government and expect others to do so.
“One of my biggest concerns has been that the ongoing focus on Mr Cummings has been detracting from the most important task, which is dealing with coronavirus and starting the process of recovery and easing lockdown.”
Mrs May is fiercely loyal to her party and her intervention demonstrates the strength of feeling on Conservative backbenches.
It highlights the deep rift Mr Johnson has opened among Tories by standing by his adviser, despite the Mirror revealing last weekend how he travelled from London to Durham, and also made a 60-mile round trip to a local beauty spot, Barnard Castle, during lockdown.
Mr Cummings claimed he went to Durham so he and his wife had access to childcare for their young son if they fell ill.
He tried to justify the journey to Barnard Castle by claiming he was testing his eyesight.
Police said he would have been turned back if he had been caught on his drive from the capital.
He may have committed a minor breach of lockdown rules with the trip to Barnard Castle, they added.
Nearly 17,000 fines for alleged breaches of coronavirus lockdown rules have been issued by police in England and Wales, according to figures yesterday(FRI) from the National Police Chiefs' Council.
But officers will take no action against Mr Cummings and the PM believes the matter is closed.