The prime minister's chief aide is said to have suffered coronavirus-like symptoms at the end of March.
Downing Street adviser Dominic Cummings is facing more questions after allegations he made a second trip to Durham during the lockdown.
Sometime towards the end of March, he travelled with his wife and child to a family home in Durham after his spouse developed coronavirus symptoms.
He said he went to the North East to be close to relatives so he would have help looking after his four-year-old child if he himself became unwell. On 30 March, Downing Street said Mr Cummings had COVID-19 signs.
It has now been reported by the Sunday Mirror and The Observer he was seen on 19 April near the property, days after being photographed in Downing Street, having returned from Durham to London.
Here is a timeline of the lockdown measures and Mr Cummings' movements:
18 March
At his Downing Street briefing the PM said: "Everyone - everyone - must follow the advice to protect themselves and their families, but also - more importantly - to protect the wider public. So stay at home for seven days if you think you have the symptoms...
"Whole household to stay at home for 14 days if one member in that household thinks he/she has the symptoms... Children should not be left with older grandparents, or older relatives, who may be particularly vulnerable or fall into some of the vulnerable groups."
22 March
Government guidance states: "People must remain in their primary residence. Not taking these steps puts additional pressure on communities and services that are already at risk...Leaving your home - the place you live - to stay at another home is not allowed."
23 March
Strict lockdown rules are imposed which mean people can only leave their houses for essential travel.
In a TV address to the nation, Boris Johnson says people must stay at home to curb the spread of coronavirus.
27 March
Boris Johnson and Health Secretary Matt Hancock are confirmed to have tested positive for coronavirus.
Mr Cummings is seen running along Downing Street shortly after the prime minister posts a video saying he has contracted the virus.
Weekend of 28 and 29 March
Over this weekend, Mr Cummings is said to have developed coronavirus symptoms.
30 March
Downing Street confirms Mr Cummings is self-isolating after developing symptoms of the virus.
31 March
According to a joint investigation by The Guardian and the Daily Mirror, Mr Cummings travelled to his family's farm in Durham - and it was on this date that Mr Cummings' family were spoken to by the police.
A spokesperson for Durham Constabulary said: "On Tuesday, March 31, our officers were made aware of reports that an individual had travelled from London to Durham and was present at an address in the city.
"Officers made contact with the owners of that address who confirmed that the individual in question was present and was self-isolating in part of the house.
"In line with national policing guidance, officers explained to the family the arrangements around self-isolation guidelines and reiterated the appropriate advice around essential travel."
Downing Street has denied the police spoke to Mr Cummings or his family - and said the aide had acted "reasonably" and in line with lockdown rules.
"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," Number 10 said in a statement.
"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."
10 April
Deputy chief medical officer Jenny Harries said being too ill to look after a small child was an "exceptional circumstance" and she pointed to accessing family support, among other options.
12 April
New reports by the Sunday Mirror suggest Mr Cummings and his family were seen walking by the River Tees in Barnard Castle, 30 miles from Durham, before getting into a car around lunchtime.
14 April
Mr Cummings is pictured in Downing Street after recovering from coronavirus symptoms
19 April
More than a fortnight after the first sighting of Mr Cummings in Durham, and five days after being photographed back at work in Downing Street, he was reportedly seen again in the northeast town.
Reports suggest that on the second visit, passers-by saw Mr Cummings at Houghall Woods, near his parents' home.
25 April
In a Spectator column, Mr Cummings's wife, Mary Wakefield, detailed his illness."Day in, day out for 10 days he lay doggo with a high fever and spasms that made the muscles lump and twitch in his legs. He could breathe, but only in a limited, shallow way."
"I felt breathless, sometimes achy, but Dom couldn't get out of bed," she said.