Dominic Cummings said he did not speak to Boris Johnson before driving to County Durham as he answered allegations that he breached coronavirus lockdown restrictions.
The Prime Minister's chief adviser said his decision to drive to 260 miles was based not only on fears over a lack of childcare if he became incapacitated with Covid-19 but also concerns about his family's safety.
The defence of his actions comes amid furious calls for him to resign or be sacked by Mr Johnson for travelling north during lockdown to self-isolate with his family after his wife developed coronavirus symptoms.
Addressing journalists in the garden at Downing Street, Mr Cummings said: “I did not ask the Prime Minister about this decision.
"He was ill himself and he had huge problems to deal with. Every day I have to exercise my judgement about things like this and decide what to discuss with him.
"I thought that I would speak to him as the situation clarified over coming days, including whether I had symptoms and whether there were tests available
"Arguably this was a mistake and I understand that some will say that I should have spoken to the Prime Minister before deciding what to do."
Mr Cummings did not apologise for his actions and said he did not regret driving his family out of London - however he did add that "reasonable people may disagree".
He also said “I have not offered to resign”, adding: “I have not considered it.”
Mr Cummings denied further reports which suggested he took a second trip to the North East on April 14.
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