United Kingdom Opposition Leader Sir Keir Starmer has trashed Boris Johnson's apology for a Downing Street party the Prime Minister held during lockdown in 2020.

In a packed chamber, Mr Johnson apologised and explained he thought the gathering was a work event and not in breach of COVID rules.

The explanation provoked fury from the Labour leader who said it was “offensive” to the British public.

"The pathetic spectacle of a man who has run out of road," he told the parliament.

"It is so ridiculous. He's finally been forced to admit what everyone knew – that when the whole country was locked down he was holding boozy parties in Downing Street."

Mr Starmer called on Mr Johnson to resign over the issue.

The Prime Minister resisted pressure to resign and has asked the Opposition not to pre-empt the outcome of an inquiry into the event.