A BBC Panorama investigation has revealed the true extent of lockdown parties in Number 10 as the Sue Gray report is set to be published.
Civil servants working inside government say they arrived for work the morning after a get-together to find bottles lying around parts of the building, bins overflowing with rubbish and empties left on the table.
They also tell of events with dozens of staff crowded together, and parties going so late that, on occasion, some ended up staying in Downing Street all night.
And they say staff mocked others who tried to stop what was going on.
The accounts come as Gray is expected to deliver her report on lockdown parties in No 10.
The senior civil servant’s report is expected to be heavily critical of the culture in No 10, which led to the repeated violations of Covid restrictions.
Potentially damaging further details, including the names of some of those who attended gatherings, are also due to be published.
Officials impacted by the Gray inquiry, including those to be named, were written to ahead of its publication, allowing them to have a chance to respond before it was finalised.
It is believed the report could be published on Wednesday, however the BBC said on Tuesday evening the senior civil servant will hand in her completed report that day, with the decision over its publication date being left up to No 10.
A Downing Street press conference is expected to be held after her findings are made public.
Prime Minister Boris Johnson is scheduled to address the 1922 Committee of backbench Tories on Wednesday. He is also due to address the Commons.
Related: America, what is it going to take? Reaction as tragedy unfolds in the States once again
