Keir Starmer has said that while Boris Johnson has “lost the moral authority to lead”, his focus was currently on Ukraine rather than forcing the prime minister to resign.
The Labor leader has previously called on Johnson to resign in the wake of the partygate revelations.
Speaking to Sky News’ Sunday program Sophy Ridge, Starmer said: “I haven’t changed my mind about Boris Johnson.
“I think he has lost the moral authority to lead. I don’t think he is fit to be our prime minister. I can’t force him to quit. Only Conservative MPs can do that.”
But Starmer added: “I have to say that, right now, my entire focus is on Ukraine and what we have to do in response to Russian aggression there.
“I think everyone will understand that my focus is on that vital issue right now.”
Westminster is still awaiting the results of the Metropolitan Police’s investigation into alleged lockdown-breaking parties held in Downing Street.
Johnson himself has been accused of attending some meetings and faces the possibility of being fined for violating his own Covid rules.
The prime minister had been under intense pressure from his own MPs and at one point seemed on the verge of being ousted.
However, Russia’s invasion of Ukraine has raised domestic pressure on Johnson, with many previously critical Conservative MPs reconsidering whether the time is right to change leaders.
Douglas Ross, the leader of the Scottish Conservatives, withdrew his demand that the prime minister resign, saying “anything else seems trivial” compared to the war in Ukraine.
This article originally appeared on HuffPost UK and has been updated.