Laura Kuenessberg has tweeted:

After @PippaCrerar and @danbloom1 scoop this morning, we're told by an attendee of drinks in No 10 on Dec 18th that there were 'several dozen' people there, with food, drink and games which went on past midnight... https://t.co/42taDI3SKu - No 10's said all rules were followed

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It will be interesting to see what the BBC do with that this evening.