Boris Johnson has reportedly been spotted cycling in London's Olympic Park - seven miles away from Downing Street.
Government guidance urges the public to stay local when exercising, and to restrict outdoor exercise to once a day.
Official government guidance states: "you should not travel outside your local area".
But it's claimed the PM was seen cycling in the park - some seven miles away - wearing a mask and a Transport for London hat, yesterday afternoon at around 2pm, along with an entourage of security guards.
It came as Mr Johnson was forced to justify travelling 100 miles from London to Bristol to visit a newly opened vaccination centre.
Mr Johnson said it was “essential that I explain to the public what we are doing to roll out the mass vaccination centres”.
He added: “Everybody should be asking themselves whether they need to be leaving home, whether they need to be doing something that could actually end up spreading the disease."
The Prime Minister's official spokesman said he had not seen reports of the sighting in the Olympic Park.
According to the Evening Standard, a source said the PM was exercising, but he did note how busy the park was and he commented on it at the meeting last night.
“He was concerned about if people were following the rules and was concerned after his cycle ride around the park.”
Mr Johnson is understood to have chaired a meeting of ministers to discuss the current lockdown later yesterday evening.
As well as Downing Street's large, private garden, the Prime Minister has access to the grounds of Buckingham Palace - where he runs and takes Dilyn, his dog, for walks.
This weekend's sighting comes after ministers backed police in stringent enforcement measures handed out to members of the public accused of flouting rules.
Matt Hancock said the majority of people are "following the rules" to stay at home, but he refused to criticise the police over complaints that some forces have been over-zealous in handing out fines.
Police tactics have come in for scrutiny after Derbyshire Police handed out £200 fines to two women who drove separately to go for a walk at a remote beauty spot situated around five miles from their homes.
The constabulary has since confirmed it will be reviewing all fixed penalty notices issued during the new national lockdown in England after it received clarification about the coronavirus regulations from the National Police Chiefs' Council (NPCC) following the incident.
Mr Hancock, asked about Derbyshire Police's approach, told Sky News' Sophy Ridge on Sunday programme: "I'm absolutely going to back the police because the challenge here is that every flex can be fatal.
"You might look at the rules and think 'Well, it doesn't matter too much if I just do this or do that'.
"But these rules are not there as boundaries to be pushed, they are the limit to what people should be doing.
"The police are right to take very seriously the rules we have brought in. We haven't brought them in because we wanted to, we've brought them in because we had to.
"Every flexibility can be fatal."
