Boris Johnson broke social distancing guidelines when Tory MPs crammed into a meeting with him, it has been claimed.
The Lib Dems are calling for an investigation after at least 50 Tories from the 1922 Committee allegedly gathered in a room, despite a sign on the door said that only 29 people should be allowed in.
Shortly after the meeting ended, his office tweeted a reminder that meetings of more than 30 people are illegal and anyone attending such a gathering could be fined £100.
The PM told the meeting he wanted people across the country to be mixing closely together in the same way by Christmas, witnesses told the Bloomberg website.
The Lib Dems have written to Commons leader Jacob Rees-Mogg to demand an inquiry and for action to be taken if rules were broken.
It has been reported that some MPs observed social distancing rules by taking seats that had been spaced out but late arrivals “crammed” together at the back of the room, according to Bloomberg.
Graham Brady, who chairs the committee, said: "It is a workplace and social distancing of one meter plus was maintained as per government guidance for other workplaces.
“Obviously it is important that the democratic process is not interrupted.”
Downing Street did not deny that Mr Johnson addressed a packed room of Tory MPs.
Repeatedly pressed on whether the rules had been broken, or why Mr Johnson had not left the room if it was too full, a Downing Street spokesman said: "I'm not privy to the detail, it's a political event."
Asked if Mr Johnson obeys his own social distancing rules, the spokesman replied: "Yes."
Shadow Commons leader Wera Hobhouse said: “Reports such as those of the 1922 Committee last night undermine faith in Government and ultimately impact the effectiveness of Government public health messaging.
“We cannot allow it to look as though there is one rule for Conservative MPs and another for the rest of the country.
The Standard has contacted the Conservative Party for comment.