Rishi Sunak accused Sir Keir Starmer of standing by Labour Rochdale by-election candidate Azhar Ali as he spoke to members of the public during a GB News forum on Monday, 12 February.
The prime minister said the Labour leader "stood by" the politician and "sent cabinet ministers to support him, until literally five minutes before I walked on tonight under enormous media pressure."
Labour withdrew its support for Mr Ali following criticism of remarks he made about Israel.
Mr Ali apologised after he was recorded suggesting that Israel allowed the October 7 Hamas assault and used it as a pretext to invade Gaza.
"The Labour Party hasn’t changed. It’s a con," Mr Sunak added.