Keir Starmer accused Rishi Sunak of having “lost his marbles” after he started a bizarre diplomatic row with Greece.
The Labour leader made fun of the prime minister for having “the reverse Midas touch”, suggesting everything he touches turns to shit.
Sunak was due to have a meeting with Greek prime minister Kyriakos Mitsotakis this week.
But the prime minister cancelled it at the last minute because Mitsotakis had reiterated his desire to see the Elgin Marbles returned to Greece during a TV interview.
The ancient artefacts were brought to Britain in the 19th century after UK ambassador Lord Elgin removed them from the Acropolis in Athens.
They now sit in the British Museum, which first received a formal request for their permanent return in 1983.
The British Museum is unable to give up ownership of the sculptures under the terms of the 1963 British Museum Act, which prohibits the removal of objects from the institution’s collection.
Speaking during PMQs, Starmer accused Sunak of “small politics” by turning down the chance to discuss “serious issues” with a Nato and economic ally at at time of global instability.
“In an effort to hide from his failures the prime minister was seen this week arguing about an ancient relic, that only a tiny minority of the British public have an interest in, but that’s enough about the Tory party,” Starmer joked.
“Never mind the British Museum. It’s the prime minister who has obviously lost his marbles.”
Starmer added: “It is ironic he has suddenly taken such an interest in Greek culture when he has clearly become the man with the reverse Midas touch.
“Everything he touches turns to... maybe the home secretary can help me out... rubbish.”
James Cleverly, the home secretary, has been embroiled in a row over either calling a northern English town “a shit hole” or a Labour MP “shit”.
Sunak defended cancelling the meeting, accusing the Greeks of breaking an agreement not to publicly discuss the ownership of the Elgin Marbles while in the UK.
And the prime minister accused Starmer of “backing an EU country over Britain” in the row, despite the Labour leader having said he did not support returning the artefacts to Greece.
“He will back Brussels over Britain every single time,” Sunak told MPs.
“Specific commitments and specific assurances on that topic were made to this country and then were broken, it may seem alien to him, by my view is when people make commitments they should keep them.”