Labour has demanded a "swift explanation" from Downing Street after newspaper reports suggested Boris Johnson's most senior adviser was spoken to by police over an apparent breach of lockdown restrictions.
A joint investigation by The Guardian and the Daily Mirror claims Dominic Cummings was approached by Durham Constabulary on 31 March after travelling to the city, which is more than 200 miles from his London home.
Sky News understands that Durham Police did not speak to Dominic Cummings directly but spoke to his parents.
A Number 10 spokesperson had confirmed on 30 March that Mr Cummings was self-isolating after suffering symptoms of coronavirus.
At the time, the government advice was that people should stay at home and not travel to second homes.
The newspapers also suggest a local resident saw Mr Cummings at the doorstep of his parents' home with a child believed to be his son on 5 April.
A Labour spokesperson said: "If accurate, the prime minister's chief adviser appears to have breached the lockdown rules. The government's guidance was very clear: stay at home and no non-essential travel.
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"The British people do not expect there to be one rule for them and another rule for Dominic Cummings.
"Number 10 needs to provide a very swift explanation for his actions."
'They will fight very hard to keep him'
Sky's deputy political editor Sam Coates said: "Dominic Cummings is an essential person in this government in the view of many people in Downing Street.
"They will fight very hard to keep him. As of now, there is no official response to these stories.
"However, there are some suggestions on social media and anonymously that Dominic Cummings was travelling to Durham because he and his wife were ill and they needed some support for their child – something they believe was permitted under the rules and guidelines set down by government."
He added: "There is going to be an almighty fight in the days to come over Dominic Cummings' future but don't expect Boris Johnson to lose him in a hurry."
The Scottish National Party's (SNP) Westminster leader Ian Blackford said Mr Cummings' position was "completely untenable", adding "he must resign or be sacked".
In a series of tweets, Mr Blackford said: "This is a key test of leadership for Boris Johnson. People must have confidence that the Tory government is following its own rules – not being investigated by the police for breaking them.
"Millions of people will find it completely incredible that Boris Johnson's most senior adviser has been breaking his own government's rules when the rest of us have all made huge sacrifices to obey them.
"There was absolutely nothing in the list of reasons under the law for leaving the house that allowed someone to travel the length of the country to stay with their parents, particularly not someone who was known to have the virus."
Sir Ed Davey, acting leader of the Liberal Democrats, has called for Mr Cummings to quit over the allegations.
He posted on Twitter: "If Dominic Cummings has broken the lockdown guidelines he will have to resign, it is as simple as that."
Breaches of lockdown restrictions have recently led to some high-profile resignations.