Dominic Cummings has said it would be “very unwise for No 10 to lie” about social events that allegedly took place during lockdown last Christmas, after the prime minister’s spokesman insisted that “there was not a party”.

Cummings, who left his role as Boris Johnson’s top aide in autumn 2020, accused his former boss of having “set the course of lying on Covid in spring when he decided to start rewriting history”. He also alleged that some political journalists were “also at parties in No 10 flat”, so were “trying to bury” the story about parties in Downing Street during lockdown.

The Mirror first revealed that two social gatherings were held in Downing Street during restrictions, including a leaving party for a former aide, Cleo Watson, in November 2020, and a Christmas party at which there were games and refreshments that went on past midnight in mid-December.

Two Labour MPs have reported this to the police. In the House of Commons on Monday, Wes Streeting, the shadow health secretary, said people in his Ilford constituency were being prosecuted for holding an indoor gathering on the same day.

Questioning Sajid Javid, the health secretary, he said: “Isn’t it time that the government comes clean about the event in Downing Street on that same day, admit they broke the rules and apologise – or does the secretary of state believe, as the prime minister appears to, that it’s one rule for them and another rule for everyone else?”

Javid replied: “In terms of rules, of course they should apply to everyone, regardless of who they are.”

Ministers have repeatedly been pressed over the gatherings in recent days, with Kit Malthouse, the policing minister, saying a party of the sort that is alleged to have taken place inside Downing Street last December might not necessarily have broken the strict lockdown rules in place at the time.

This contradicted comments made by Dominic Raab, the justice secretary, who conceded on Sunday that a “formal party” of the sort reported would have been contrary to the then Covid-19 guidance.

Amid the confusion, Downing Street hardened its language on the affair, having previously responded by insisting: “All Covid rules were followed.”

The prime minister’s official spokesman declined to say whether an internal investigation had been carried out, but told reporters: “There was not a party, and Covid rules have been followed at all times.”