Is there anything Cummings could say that would make people angry with Boris?

The prime minister has been raked over the coals for Covid-19 failings a number of times, but little has appeared to damage his public standing

Dominic Cummings has promised to answer questions for ‘as long as the MPs want’ (Getty)

We have reached D-day, for Dominic – as Cummings would no doubt smirk to see it styled. Are we in for a no-holds-barred morning of reflection and revelations, or a damp squib?

There is little doubt that parts of the testimony of the former chief adviser to Boris Johnson will be embarrassing for the prime minister and Labour will jump on anything they can. The fact that Cummings will begin at 9.30, giving plenty of time before Johnson and Keir Starmer face off at Prime Minister's Questions to catch a couple of hours of testimony will have been noted by the Opposition.

As for how uncomfortable it will be for Cummings, he is likely to try and bat off questions with the same detached air that he has been seeking to cultivate for years. They will be grandstanding – there always is on these occasions – but the chairs of the two committees Cummings faces, Jeremy Hunt and Greg Clark, will be no pushovers.

Hunt ran the department of health for six years, while the former business secretary Clark has written for us before that every facet of the pandemic needs to be examined for the lessons it could yield. That Clark was was reportedly on the end of foul-mouthed threats from Cummings during the Brexit withdrawal period only adds to the sense that Cummings should not expect an easy morning.

When it comes to the content of Cummings's answers, there is plenty that will merely add to an extensive picture that has been built up over the last few months. Issues such as the timing of lockdowns – were we too late? – to herd immunity, have already had plenty of ink spilt over them. There is one element over lockdown that could cause the PM considerable problems. If Cummings tries to track back on Johnson's denials over reports that he said he would prefer to see “bodies pile up in the streets” than a third lockdown, then that will be part of the news agenda for days. Johnson has called the reports "total rubbish".

Beyond that, questions over testing will remind the public of what a mess that was for months and there will be other elements of the Covid-19 response and its failings that the government has already managed to move past once.

MPs will jump on the line at the end of Cummings's most recent blog post, that: "It is sad to see the PM and his office fall so far below the standards of competence and integrity the country deserves." Questions around Johnson's fitness for office could be very awkward for the prime minister – depending on how candid Cummings is. But, Johnson has faced multiple such attacks from Labour on those very issues and it appears to have done little to harm his standing with the public.

As so often with this government, the biggest threat to Johnson from the testimony of Cummings may come from the element of surprise. Cummings has always sought to portray himself as a maverick– and Johnson could face the full extent of that.

However, could Cummings deal Johnson real political damage? The chance is there, but the evidence throughout the last 12 months is that it would take something very significant to take the wind out of the prime minister's sails. If it hasn't happened yet, there is likely little Cummings can say to change that.