Boris Johnson's top adviser has faced calls to resign after travelling 260 miles during lockdown, in order to get help looking after his child.
The prime minister said Dominic Cummings had "acted responsibly, legally and with integrity". So, what are the rules and how have they been applied?
What is the relevant coronavirus guidance?
Government advice for households where one or more members have coronavirus symptoms is simple - stay at home.
Official guidance published in March says "it is very important that individuals with symptoms that may be due to coronavirus and their household members stay at home". This still applies.
The guidance outlines ways to pass the time and obtain food and medicine.
However, it does acknowledge that it is not always straightforward when children are involved.
It says: "If you have children, keep following this advice to the best of your ability, however, we are aware that not all these measures will be possible."
Has the advice changed?
The guidance has been on the government website since 12 March, before lockdown was imposed.
The day after lockdown began, 24 March, the deputy chief medical officer for England, Dr Jenny Harries, clarified who could look after a child if both parents or carers were incapacitated.
She said: "Clearly if you have adults who are unable to look after a small child, that is an exceptional circumstance.
"And if the individuals do not have access to care support - formal care support - or to family, they will be able to work through their local authority hubs."
Has Dominic Cummings broken the rules?
Any of the government lockdown guidance can be overruled by safeguarding concerns, or prevention of harm, Dr Harries said at Saturday's briefing.
She used the examples of an elderly person with no supply of medication, or a child with both parents too unwell to provide medical care.
"Risk to life" would be a valid reason to break lockdown rules, Dr Harries said.
When Dominic Cummings decided to travel from London to Durham, to stay near his relatives for support, only his wife was displaying coronavirus symptoms. So, he could have cared for their child himself.
But Transport Secretary Grant Shapps said at Saturday's briefing that the welfare of a four-year-old child was the main thing. He said Mr Cummings' actions had prevented the child from being without any support, should things have become worse.
Mr Shapps was asked by Andrew Marr on Sunday whether there was a risk to life in Mr Cummings' situation.
The transport secretary said that "they would have felt they had to put some measures in place" and added that Mr Cummings' four-year-old child could not feed and bathe himself.
Speaking at Sunday's briefing, the PM said he had spoken to Mr Cummings and concluded he had "no alternative" but to travel to the North East for childcare "when both he and his wife were about to be incapacitated by coronavirus".
What does the government say parents should do?
Mr Shapps said that government guidance was to keep following the advice to best of your ability.
He acknowledged that not all measures would be possible, depending on the circumstances of each family.
He said that Mr Cummings was worried about his ability to care for his child and that another location, with family help, was a better place for him to settle and stay for the duration of his illness.
The government stressed that there was no longer any restriction on how far people can drive - for example to take exercise - but that those who had symptoms should remove themselves from the wider population.
The government says that Mr Cummings was able to stay in a separate property near to his parents and sister and so did not have to mix households - something not everyone would have the means to do.