The Liberal Democrats demanded an investigation after at least 50 Tories are thought to have crammed into a room – despite a sign on the door warning that only 29 should be allowed.
The prime minister is said to have told the meeting that he wanted people across the country to be mixing closely together in the same way by Christmas, witnesses told the Bloomberg website.
Yet, just 40 minutes after it finished, the prime minister’s office issued a tweet warning people not to attend gatherings of more than 30 people.
“There is no end to the Tories’ hypocrisy,” protested Wera Hobhouse, a Liberal Democrat MP.
“The prime minister and his ministers have already evaporated the public’s trust in them with their shameless defence of Dominic Cummings, but it appears they have not learned their lesson.”
The Lib Dems have written to Jacob Rees-Mogg, the leader of the House of Commons, to demand an inquiry and for action to be taken if rules were broken.
The controversy comes after Mr Cummings was allowed to stay on as Mr Johnson’s chief aide despite flouting lockdown rules with his April trip to and around County Durham.
At the start of the pandemic, the prime minister boasted he was “shaking hands with everybody” and would continue to do so – despite his own scientists warning against it.
The Independent has asked Downing Street to respond to the claim that the meeting, of the 1922 committee of backbench Tories, broke coronavirus restrictions.
Gatherings of more than 30 people are illegal. Breaking the rules could cost you thousands.
If you attend an illegal gathering, you could be fined £100, increasing on each offence up to £3,200. pic.twitter.com/4QXz0FQ3hL— UK Prime Minister (@10DowningStreet)September 2, 2020
People present at the meeting reported that social distancing rules – stating that they should stay more than one metre apart – were initially observed, with seats spaced out.
But three people present, who asked not to be identified because the meeting was private, said that later arrivals “crammed” together at the back of the room to hear Mr Johnson.
Labour has continued with remote meetings of its MPs, but the Tories returned to physical gatherings after backbench criticism of the blizzard of recent policy U-turns.
Graham Brady, the chair of the 1922 committee, insisted that social distancing rules were observed at the meeting.
“It is a workplace, and social distancing of one metre plus was maintained as per government guidance for other workplaces,” he told Bloomberg.
“Obviously, it is important that the democratic process is not interrupted.”
Asked about the event, a Downing Street spokesperson said that, as a civil servant, he was not able to respond to the allegation because it was ”a political event”.
Asked whether Mr Johnson obeys his own social distancing rules, the spokesperson replied: “Yes.”