The footage shows officials - including his former press secretary - joking that the event last December was a business meeting.
The Prime Minister's raised the case himself in the Commons.
He's ordered an investigation but says he's been assured there was no party.
Labour leader Sir Keir Starmer says he's taking the public for fools.
Meanwhile Brentofrd MP Ruth Cadbury says she’s heard “many heart-breaking stories” stories from people across Hounslow who’ve been bereaved due to Covid.
She says there now “anger and anguish at a government which laughed about breaking breaking the rules