Dominic Cummings claims he behaved "reasonably" and "legally" when he travelled from his London home to Durham during lockdown.
An investigation by the Mirror and Guardian revealed that Boris Johnson's top adviser had been interviewed by police after reports he had broken lockdown rules.
Mr Cummings was seen by witnesses at his parents home in Durham at the end of March, when he was supposedly isolating with coronavirus symptoms at his London home.
A statement issued by Downing Street on Saturday morning defended the Prime Minister's chief-of-staff, with several cabinet ministers tweeting their support.