Martin Reynolds boasted that they had "got away with" partygate rule-breaking, in email and WhatsApp exchanges outlined in Sue Gray's report.
Ms Gray's report concluded that the gatherings that where held in No 10 where "not in line with Covid guidance at the time".
The then Principal Private Secretary, Mr Reynolds arranged a gathering in the gardens of No 10 on May 20 2020. At the time leaving home without a reasonable excuse was prohibited.
The Partygate inquiry outlined that some individuals had expressed concerns about whether the timing of the event was appropriate.
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Martin Reynolds (back, far left), was ousted amid outrage over partygate scandal
Jeremy Selwyn/Evening Standard
An email was distributed to around 200 Downing Street staff on behalf of Mr Reynolds, inviting people to make the most of the "lovely weather" with some "socially distanced drinks in the garden this evening".
The email concluded with: "Please join us from 6pm and bring your own booze!"
Lee Cain, then-No 10 Communications Director replied to Mr Reynolds saying: "I'm sure it will be fine – and I applaud the gesture". But he noted it represented "somewhat of a comms risk in the current environment".
The report refrained from stating the exact number of attendees at the event, but it estimated that around 30 to 40 people where present, including the Prime Minister for around 30 minutes.
Staff indulged in "Drinks and pizza" which was provided and paid for by staff, with many individuals leaving between 10pm and 11pm.
Following the event, a No 10 special adviser thanks Mr Reynolds for "providing the wine", saying it was "a very kind thing to do and I know everyone really appreciated it".
The event was referenced again in another WhatsApp exchange to a special adviser on an unknown date, where Mr Reynolds wrote: "Best of luck – a complete non story but better than them focusing on our drinks (which we seem to have got away with).”
He was subsequently ousted amid outrage over the Partygate scandal.
Mr Reynolds is reportedly being lined up to become the UK’s next ambassador to Saudi Arabia.