The former top aide will give evidence to a joint committee of MPs investigating the government’s response to the coronavirus crisis next month.
A source told the paper: “Dominic has copies of everything and knows where all the bodies are buried.
“He was pushing the prime minister hard to lock down sooner in the autumn and he has lots of evidence that shows that his decision to delay led to devastating consequences.”
Downing Street is also concerned that Mr Cummings might expose details about Mr Johnson’s life with fiancee Carrie Symonds.
Last night Mr Cummings suggested the government was too slow to close the borders when the pandemic started.
He said the scientific consensus that travel bans would not help prevent the spread of Covid-19 was flawed.
In response to a tweet about how Vietnam had protected its borders he said it was a “very important issue re learning from the disaster”.
His tweet followed a lengthy blog post where he openly attacked Mr Johnson and claimed that the manner in which he obtained funding for the refurbishment of his Downing Street flat was “unethical” and “possibly illegal”.
Mr Cummings claimed Mr Johnson had attempted to secure funding from Conservative supporters for £58,000 worth of renovations to the flat he shared with Ms Symonds.
The prime minister said on Friday he had personally paid back the money.
Mr Cummings also accused Mr Johnson of trying to block an inquiry that implicated Henry Newman, a friend of Ms Symonds, after details of the autumn lockdown were leaked to the press.
The blog post came after Mr Johnson blamed Mr Cummings for leaking texts he sent to James Dyson regarding a tax waiver.
Jeremy Hunt, the chairman of one of the committees that will question Mr Cummings told the Sunday Telegraph that MPs would would publish whatever the former Downing Street aide gave them as long as it did not put national security at risk and as long as the MPs on the committee agree.
Mr Hunt said: “We will publish whatever he gives us – we would have to check if it passes any tests.”
Downing Street insiders have no idea the extent of the material Mr Cummings claims to have and say they are “terrified” about further revelations.
One source said there is extreme nervousness about an apparent “treasure trove” of embarrassing documents that Mr Cummings might seek to get published.
Mr Cummings quit 10 Downing Street last November after an apparent power struggle involving Ms Symonds.