Downing Street parties: The unanswered questions

Boris Johnson is under intense pressure following fresh revelations of a drinks party in the No 10 garden during the first lockdown in May 2020.

Senior civil servant Sue Gray is tasked with investigating the ins and outs of alleged gatherings of Westminster's most powerful residents and staff.

But what questions face her, and the prime minister?

The main question on everyone's lips that remains unanswered is whether the PM attended the garden party on 20 May 2020, when tough restrictions were in place.

Eye witnesses from the event told the BBC he was there with his wife, Carrie.

But so far, Mr Johnson has declined to answer the question himself, saying all will be revealed in Ms Gray's investigation.

An email from Mr Johnson's principal private secretary, Martin Reynolds, inviting people to "make the most of the lovely weather", was sent to a distribution list of around 100 people.

But the full list of recipients hasn't been published.

So why does it matter who was on the list?

Well, the names will show who knew about the party taking place.

Another question being posed over the garden drinks is whether the email from the prime minister's principal private secretary or PPS could have gone out without Mr Johnson knowing about it.

Caroline Slocock, who worked in the private offices of Margaret Thatcher and John Major, told BBC Radio 4 it was "inconceivable" the PM wasn't aware of such an invite, especially one from a close staff member using the word "we".

Hannah White from the Institute for Government - and former secretary to the Committee on Standards in Public Life - also said she believed the PM "had to have" known about the event being organised by his PPS.

So even if Mr Johnson did not attend the event, some believe he would have known about it.

The next step is to find out who chose to go to the gathering, despite the lockdown.

The BBC has been told from sources at the garden drinks that around 30 people were present, alongside the PM and his wife.

Who went to the party will be key for the same reason as the invite list, showing who knew about the event.

But more importantly, the attendee list will show who decided to break the rules - and perhaps the law - individually.

The party from 20 May is far from the only allegation of a party in Westminster during the pandemic.

But we cannot yet be certain how many gatherings took place in Downing Street and across government departments.

So far though, we know of at least 10 allegations that have come to light.

During that first lockdown in May 2020, there are two incidents in question - one on 15 May, pictured in the Guardian with the PM and his wife sharing wine and cheese with staff that was claimed to be a work meeting, and the most recent allegation of the "bring your own booze" garden party.

In November of the same year, there are claims the PM's wife, Carrie Johnson, held a party in the flat above No 10, as well as allegations staff held a leaving do for a staff member, with Mr Johnson making a speech.

And in December, there were said to be festive quizzes and Christmas parties in several places.

One was attended by the PM virtually, but he insisted all the guidance was followed to the letter.