Boris Johnson's former adviser is giving evidence to a joint inquiry of the Commons Health and Social Care and Science and Technology committees on Wednesday.
According to ITV News Politics Editor Robert Peston, Cummings' appearance will be a "box office politically", as the former aide plans to prosecute the prime minister and his scientific advisers for failing to lock down early enough in March 2020, and Mr Johnson and Rishi Sunak for failing to lock down in early September.
Here's what we can expect in Cummings' evidence on Wednesday:
Did the lockdown come soon enough?
Cummings is known to have supported tougher lockdowns and it has been suggested Boris Johnson did not want to lock down too early.
Earlier this week, Cummings tweeted fresh allegations that on March 14 last year, one of the things being “screamed at” Mr Johnson was that there was “no plan for lockdown” and “our current official plan will kill at least 250k and destroy the NHS”.
And Cummings is expected to claim the Prime Minister delayed the lockdown in September after saying “Covid is only killing 80-year-olds”.
Cummings will outline how Mr Johnson did not wish to repeat what he saw as his mistake from March and said: “I’m going to be the mayor of Jaws, like I should have been in March.”
The former advisor claimed the Scientific Advisory Group for Emergencies (Sage) was split over whether to lockdown as late as March 18, with Department of Health and Social Care officials reportedly saying “lockdown just means it pops back up again in second wave so why change strategy?”.
He also suggested further lockdown could have been avoided if mass testing had been developed properly earlier.
Cummings tweeted: “If we’d had the right preparations + competent people in charge, we wd probably have avoided lockdown1, *definitely* no need for lockdowns 2&3. Given the plan was AWOL/disaster + awful decisions delayed everything, lockdown1 became necessary”.
Was herd immunity government policy?
Government ministers said herd immunity was not a tactic the government looked to use at the start of the pandemic.
But Cummings claimed that the pandemic preparation plan had outlined that the strategy was to have one peak of the disease, before reaching herd immunity by September.
He said the policy, which would allow the virus to spread, was dropped in March last year after a warning it would lead to a “catastrophe”.
Dr Jenny Harries, who was deputy chief medical officer for England at the time, previously said: “I can categorically say I have never been in any government meeting where herd immunity was put forward at that point of the pandemic as a mechanism of control.”
Cummings on Twitter dismissed government denials at the time as “bull****” and said Downing Street had chosen to lie, which he said was a “very foolish” move that demonstrated “appalling ethics”.
He also hinted he may have evidence to back his claims.
Has the government been transparent enough?
Cummings claimed “secrecy contributed greatly to the catastrophe” in February and March last year.
Cummings said “openness to scrutiny would have exposed government errors weeks earlier than happened” and that public scrutiny of plans would help stop a situation where vaccines do not have an impact on new variants.
“This will hopefully show it’s been taken seriously,” he tweeted. “If not, better learn now that the Gvt has screwed up again than when ‘variant escapes’ news breaks.”
He added: “I can think of no significant element of Covid response that wd not have been improved by discarding secrecy and opening up.”
And he said that having seen the classified elements of the response, some 99% of vaccine plans could be made public without rising national security.
He also called for the minutes of Sage meetings to better reflect the exchanges which happened there.
Was the government prepared for a pandemic?
Cummings said the plan to tackle coronavirus “was supposed to be ‘world class’, but turned out to be part disaster, part non-existent”.
He said MPs should push for the government to be more open about plans for “more dangerous things than Covid… before we find out the hard way they’re as ‘world class’ as the Covid plan”.
In October 2016, the Government carried out Exercise Cygnus, which aimed to test plans for a future “worst-case-scenario” flu pandemic affecting up to 50% of the population and causing 200,000 to 400,000 excess deaths.
But former health secretary Jeremy Hunt has admitted the UK prepared for the wrong type of pandemic.
What can be learned from the public inquiry?
Cummings has supported a public inquiry but said he fears it will not get answers.
He said on Twitter: “If SW1 wanted to ‘learn’ there wd already be a serious exercise under way. The point of the inquiry is the opposite of learning, it is to delay scrutiny, preserve the broken system & distract public from real Qs, leaving the parties & senior civil service essentially untouched”.
Mr Johnson said earlier this month there would be an independent public inquiry into the handling of the pandemic.
The inquiry will be able to take oral evidence under oath, and he said the state has an obligation “to learn every lesson for the future”.
Did the Government close the borders soon enough?
As the government was recently criticised for the apparent delay in closing borders as the Indian variant grew in risk, Cummings described the early policy at airports as a “joke”.
Home Secretary Priti Patel said she advocated closing the UK’s borders in March last year, but said she was overruled, as the balance between public health and the economy was weighed up.
One paper considered by Sage in April said there was little justification for closing borders while case numbers were high, with imported infections representing a tiny proportion of cases.
In a tweet on May 17, Cummings said: “There’s a general western problem based on nonsense memes like ‘Asians all do as they’re told it won’t work here’.
“This is what many behavioural science ‘experts’/charlatans argued, disastrously, in Feb2020. This nonsense is still influencing policy, eg our joke borders policy”.
Did Boris Johnson miss key Covid meetings to write a book about Shakespeare?
Johnson did not chair the first five meetings of the Cobra emergency committee in January and February 2020.
The Sunday Times newspaper suggested officials fear Cummings will use his appearance before MPs to accuse Johnson of missing the meetings because he was working on a biography of Shakespeare, as he needed the money to fund his divorce from Marina Wheeler, his second wife.
Asked if the prime minister had spent time on the book, his spokesman said: “No, not that I’m aware of.”
He added the prime minister had been “ensuring the public are kept as protected as possible during this global pandemic”.
Responding to claims Johnson had missed Cobra meetings to write his book, the spokesman said: “No, and I think there are a number of incidents I can run you through where Cobras have been chaired by relevant secretaries of state.”
How about his own involvement?
People have also been asking why Cummings, who left government in November, did not do more as the prime minister's closest adviser.
MPs may ask Cummings how he could be seemingly powerless in the government's handling of the pandemic.
Asked on Monday if Johnson believed Cummings was a liar, following the outpouring of allegations, the spokesman said: “I haven’t asked him that question.”