Sir Keir Starmer has said he will not listen to advice from the Conservative Party as voters "rejected them profoundly".
The new prime minister initially struck a cordial tone with his predecessor at his first Prime Minister's Questions after achieving a landslide victory.
But he gave the Conservatives some advice on changing their party just hours before nominations open for the Conservative leadership race this evening.
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Sir Keir and Rishi Sunak agreed to keep each other informed on Ukraine developments after Mr Sunak joked Team GB Olympians probably did not want to hear from him about how to win.
However, during questions from MPs, Sir Keir upped the ante as he repeatedly said there had been "14 years of failure" under the Conservative government.
And he used his final response to dig the knife in deeper to dismiss any criticism or advice from Conservative MPs.
"We're not going to listen to the party opposite," Sir Keir said.
"They put their case to the electorate. The electorate rejected them profoundly.
"And my advice would be, having sat at that despatch box for four and a half long years is when you get rejected that profoundly by the electorate it's best not to go back to the electorate and tell them that they were wrong.
"It's best to reflect and change your approach and change your party."
Sir Keir's first PMQs took place the afternoon after the prime minister faced a rebellion over an SNP vote aimed at lifting the two-child benefit cap.
He swiftly suspended seven of his MPs from the Labour Party after they rebelled and voted with the SNP - and against the government.
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The PM used an accusatory question from SNP Westminster leader Stephen Flynn about the cap to say how former Labour leader Gordon Brown's government had "lifted millions of children out of poverty".
"This government will approach the question with the same vigour with our new taskforce," he said.
"Already we've taken steps, breakfast clubs, abolishing no fault evictions, decent homes."
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