Cummings was behind Vote Leave's success in the EU referendum and BoJo's election victory in December 2019.
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Does Dominic Cummings have coronavirus?
Dominic Cummings has been self-isolating after developing symptoms of coronavirus at the end of March.
He follows in the footsteps of Prime Minister Boris Johnson and Health Secretary Matt Hancock.
Why has he been asked to resign?
Cummings has been accused of being in breach of the coronavirus rules, by making non essential travel and leaving home.
He and his wife, journalist Mary Wakefield, reportedly stayed at his parents' home in Durham while self-isolating.
However, the couple have said they needed childcare help and said they stayed in a separate building at the property.
In an official statement from Downing Street, the Prime Minister has given his backing to the aide.
A No10 spokesperson said: "Owing to his wife being infected with suspected coronavirus and the high likelihood that he would himself become unwell, it was essential for Dominic Cummings to ensure his young child could be properly cared for.
"His sister and nieces had volunteered to help so he went to a house near to but separate from his extended family in case their help was needed.
"His sister shopped for the family and left everything outside.
"His actions were in line with coronavirus guidelines.
"Mr Cummings believes he behaved reasonably and legally."
The revelation comes despite No10 telling Brits they must stay at home and not see family to slow the spread of Covid.
The move allegedly went against advice, which became law on March 26, which stated: “You should not be visiting family members who do not live in your home.”
Only in exceptional circumstances were people allowed to attend relatives' addresses; for example, to drop off food or medicine to their door.
Tory MPs are said to be privately angry, but a close friend of Dominic Cummings said: "He isn't remotely bothered by this story…
"…There is zero chance of him resigning."
Acting Liberal Democrat leader Sir Ed Davey today called for Mr Cummings to explain himself – or resign.
He said: "If Dominic Cummings has broken the lockdown guidelines, he will have to resign. It's as simple as that."
Who is Dominic Cummings?
Dominic Cummings was seen as the mastermind of the Brexit campaign.
He is a political adviser and strategist, and served as the Campaign Director of Vote Leave.
Cummings is a former special adviser to Michael Gove – under Boris Johnson, he worked as the PM's senior adviser.
Born in Durham, he is the son of an oil rig project manager and a special needs teacher.
Cummings attended Durham School and Exeter College, Oxford, graduating in 1994 with a First in Ancient and Modern History.
In 2011, he married Mary Wakefield, deputy editor of The Spectator.
When did he join the Vote Leave campaign?
Cummings became Campaign Director of Vote Leave upon the creation of the organisation in October 2015.
He is credited with having created the official slogan of Vote Leave, "Take back control" and with being the leading strategist of the campaign.
Cummings was questioned and criticised by MPs at the Treasury Select Committee in April 2016 for creating misleading leaflets for the Leave campaign.
His campaign strategy was summarised as: "Don’t talk about immigration"; "Do talk about business"; "Don’t make the referendum final"; "Do keep mentioning the Charter of Fundamental Rights and the over-reach of the European Union’s Court of Justice".
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Vote Leave emerged victorious in the June 2016 referendum which resulted in a 52 per cent vote to leave the European Union.
He was named as one of "Debrett's 500 2016" people of influence.
He used data-driven campaigning to win over undecided voters by pushing a small number of key messages – and came up with the slogan "take back control".