- Dominic Cummings said a senior UK official held a drinks party in May 2020 against lockdown rules.
- Cummings, a former top aide to Johnson, said he objected and tried to stop it.
- Johnson's authority has been rocked by claims his officials ignored the rules they put in place.
Dominic Cummings explosively claimed that another, previously unreported party took place at Downing Street in breach of UK lockdown rules, as he sought to downplay reports of his attendance at a gathering.
The former chief aide to Boris Johnson was shown in the garden of Number 10 in May 2020 in aphoto published by the Daily Mirror.
He argued that it was in fact a continuation of a meeting in which the government COVID strategy and "domestic priorities" were being discussed over a bottle of wine.
It was "in no sense a party or organized drinks", he said, arguing that he often held work events outside for better ventilation.
Writing on his Substack blog, Cummings said that more significant than the photographed gathering was another event.
"There was a social event May 2020 that should not have happened", he said, and claimed that an unnamed senior Number 10 official "invited people to 'socially distanced drinks' in the garden".
This would have been at the tailend of the first lockdown, when people were banned from socialising, even outdoors.
He wrote: "I and at least one other spad (in writing so Sue Gray can dig up the original email and the warning) said that this seemed to be against the rules and should not happen.
"We were ignored. I was ill and went home to bed early that afternoon but am told this event definitely happened."
Johnson has been rocked by claims of successive lockdown-breaching parties taking place at Number 10 and across other departments, as well as at CCHQ.
In December, Cabinet Secretary Simon Case was forced to recuse himself from leading an investigation into gatherings across Whitehall after it emerged that a Christmas quiz had been held at his department.
Sue Gray, a senior civil servant, is now leading the probe, which could be expanded to include any relevant allegation.
Cummings said: "Officials I spoke to in 2021 said to me and others that there were various parties after I left and the PM was aware of them. I have also been told there are other photos of other parties against the rules in 2021, some picturing the PM."
Number 10 did not immediately reply to Insider's request for comment.