Tens of thousands of people died needlessly during the pandemic and it is “intolerable” to delay a public inquiry, Dominic Cummings said.
Boris Johnson has committed to an inquiry which will start in spring 2022, but his former aide Mr Cummings said it should happen sooner.
He also said he could not imagine why Mr Johnson has not met bereaved families.
Mr Cummings said the idea that the inquiry will not start until next year is “completely terrible” and warned that memories would be rewritten and official documents would go “astray”.
“Tens of thousands of people died who didn’t need to die,” he told MPs.
“There is absolutely no excuse for delaying that because a lot of the reasons for why that happened are still in place now.
“Look at the whole debate about variants and whatnot – this has to be honestly explained.
“If No 10 today won’t tell the truth about the official plan which they briefed the media about and described on TV a year ago, what on earth else is going on in there now?”
He suggested MPs should seek to seize control of the issue and say “it’s intolerable that this can be delayed”.
He added: “There is absolutely no excuse for a delay and the longer it is delayed, the more people will rewrite memories, the more documents will go astray, the more the whole thing will just become cancerous.”
Asked why the Prime Minister would not meet bereaved families, he said: “I can’t imagine why.”
Labour leader Sir Keir Starmer said Mr Cummings’ comments about the “tens of thousands” who died was a “devastating admission”.
“Very serious allegations have been made against Boris Johnson and his handling of Covid,” Sir Keir said.
“No more delays. A public inquiry needs to start this summer.”