Eagle-eyed online critics have spotted Boris Johnson marking an 11am one-minute silence for the victims of the Plymouth shooting, while his wristwatch said 11.14am.
The Prime Minister's Twitter account posted the image of him standing solemnly in front of a clock after it struck 11am.
But the later time on his watch prompted a flurry of online accusations that he had lied, with one Twitter user claiming: "They cared enough to turn back the clock on the mantelpiece but forgot his wrist watch."
A Downing Street official, however, insisted the photo was definitely taken at 11am - and the PM's watch was simply running 14 minutes fast.
As writer Tracy King put it: “I would go with ‘the prime minister sets his watch 15 minutes late to ensure he is early for meetings’".
There was a heartfelt plea for change today as hundreds gathered in Plymouth to pay their respects to the five people killed in one of the UK's worst mass shootings.
Civic leaders, religious figures, politicians, emergency service workers and the military joined around 200 people outside the Guildhall in Plymouth city centre at 11am.
They gathered to mourn and reflect on last week's devastating events when gunman Jake Davison, 22, launched his murderous spree in the Keyham area of the city.
Davison shot his 51-year-old mother Maxine Davison, also known as Maxine Chapman, at a house in Biddick Drive before he went into the street and shot dead Sophie Martyn, aged three, and her father, Lee Martyn, 43.
In the 12-minute attack, Davison then killed Stephen Washington, 59, in a nearby park before shooting 66-year-old Kate Shepherd, who later died at Derriford Hospital.
The Prime Minister earlier branded the attack "absolutely appalling" and the government announced people who apply for a gun licence will be subjected to social media checks.
Questions have mounted over how Keyham gunman Jake Davison, 22, obtained a firearms licence and carried out his spree, killing five people before turning the gun on himself.
The family of victim Stephen Washington, 59, said their world "has been turned upside down in the blink of an eye".
The Government said on Sunday that it was preparing statutory guidance to help ensure higher standards of decision-making for police firearms licensing applications.
This will cover social media checks of those applying for permission to own a firearm or shotgun, according to the Home Office.
All police forces in England and Wales are being asked to review their current firearm application processes, as well as assess whether they need to revisit any existing licences.
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