Boris Johnson says no Covid rules were broken after reports Christmas parties were held in Downing Street at the height of last year's lockdown.
Labour leader Sir Keir Starmer accused the PM of hypocrisy for flouting the rules he had ordered the rest of the country to follow.
It follows a Mirror newspaper report of drinks parties and quizzes in November and December last year.
The prime minister did not deny parties had taken place.
But he said "all guidance was followed completely".
According to the Mirror, the official No 10 staff Christmas party was cancelled last year, but an unofficial party, which the PM did not attend, took place on 18 December.
Aides packed into a room for drinks, a Christmas quiz and a Secret Santa, the newspaper claims.
A Downing Street spokeswoman said they "don't recognise this report" and "Covid rules have been followed at all times".
The BBC's deputy political editor Vicki Young said Downing Street was very reluctant to answer detailed questions about exactly what went on, but they did not deny parties took place.
London was placed under Tier 3 lockdown restrictions on 14 December last year, after which time it was illegal to mix indoors with anyone outside your household or support bubble.
At Prime Minister's Questions, Sir Keir said: "Does the prime minister really expect the country to believe that while people were banned from seeing their loved ones at Christmas last year, it was fine for him and his friends to throw a boozy party in Downing Street?"
Mr Johnson said the rules had been followed and took a swipe at Sir Keir's reported disagreements with Labour's deputy leader Angela Rayner.
"Can I recommend to (him) that he does the same with his own Christmas party, which is advertised for 15 December, to which unaccountably he's failed to invite the deputy leader" said the PM.
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