Sir Keir Starmer insists it is important to listen to those who no longer vote Labour if his party is to regain power.
It comes as the Labour leader urged Boris Johnson to “get on and deliver” his promise of an “oven-ready” Brexit deal.
He also said his party is now showing leadership in tackling anti-Semitism but is happy to be judged on his actions rather than his words on the issue.
Speaking on Sky News’ Sophy Ridge programme, he said: “We are making it clear we’re a new leadership and that means being absolutely clear about recognising the scale of the defeat last December.
“That was devastating for the Labour Party, devastating for the Labour movement and for the millions of people who desperately needed Labour government.
“So, recognising that, listening to those that no longer vote Labour, and I’ve spent the last six months listening and asking for conversations with people that are difficult rather than easy, and changing and focusing on the future.
“That means difficult decisions like tackling anti-Semitism. So, a new leadership focused on 2024, but absolutely recognising the scale of the task we face.”
Asked what the difference is in the party under the new leadership, Sir Keir said: “The big difference is recognising we’ve lost not just one election, but four.
“Recognising that we have got to listen to those that used to vote Labour, don’t vote Labour any more, or those that have never voted Labour.
“But we have to be focused on winning the next general election in 2024.”
He added: “Leadership was necessary on anti-Semitism and that’s what we’re showing in the Labour Party now.”
Asked if the party had been lacking leadership on anti-Semitism, he said: “I think that the leadership issue is tied up with anti-Semitism.
“What I’ve tried to do as leader of the Labour Party is make it very clear in my acceptance speech (in becoming leader) that we would tear out anti-Semitism and then get on and do it, and make sure that we’re taking action as well as words.
“In all my discussions with Jewish communities they’ve said to me, ‘Keir, in the end we’ll judge you on what you do, not what you say’, and I’m happy with that.”
The Labour leader also said it is in the national interest for the UK to secure a Brexit deal.
He said: “The Prime Minister promised us there was an ‘oven-ready’ deal and he needs to get on and deliver on that promise.
“If he fails to do so, then he owns that failure and the distraction, frankly, of reopening old wounds, going back on agreements that have been made, is a distraction.
“It’s in the national interest to get a deal. I say to the Prime Minister, ‘go on, get that deal’.”
Asked if his party would back any deal, he explained: “We will look at what comes back, but if it’s in the best interests of the country, then we’ll look at it, of course we will, because a deal is in the national interest.”