Sir Keir Starmer has said it will take time to turn the country around, telling voters to judge him at the next general election.
The prime minister told the BBC his government had made “good steps”, particularly on the cost-of-living, but “we need to do more”.
It comes after a dismal few weeks for the PM, who has faced growing criticism and speculation he could face a leadership challenge.
The government is also facing a difficult Budget next week, when the chancellor is widely expected to increase taxes.
In an interview with the BBC’s Chris Mason in Johannesburg, South Africa, where the PM is attending the G20 summit of world leaders, Sir Keir was challenged over why some opinion polls suggest he is the most unpopular prime minister since modern polling began.
“We won an election last year on the manifesto that said we would change the country after 14 years of failure,” he said.
“I always said that would take time because you can’t turn around 14 years of failure in just 12 months or 16 months.
“I’m very conscious that we have to deliver on three things above all else. The first is making sure people feel better off, and that’s bearing down on the cost-of-living, making sure the public services are better, in particular the NHS, which is why we put record investment in the NHS, and making sure people feel more safe and secure.
“And I have no doubt that I will rightly be judged against that at the next election.”
Sir Keir has insisted he will lead Labour into the next general election, which is not due until 2029, although he could choose to call one earlier.
Last week, allies of the prime minister told journalists that he would fight any attempts by Labour MPs to remove him, with Health Secretary Wes Streeting among those named as plotting a leadership challenge.
However, the attempt to strengthen Sir Keir’s position appeared to backfire as it brought talk of threats to his leadership into the open and sparked further criticism of the PM.
Streeting denied he was planning to challenge Sir Keir and hit out at a “toxic” culture within No 10, although he said he did not think the PM was behind the briefings.
Sir Keir has insisted the attacks against Streeting had not come from Downing Street.
Meanwhile, the PM has faced claims from the the Conservatives his government’s Budget is already unravelling, after the chancellor backed away from raising income tax rates – a move which would break an election pledge.
Asked if he was frustrated the achievements of his government were being “drowned out”, Sir Keir told the BBC: “Every minute that is spent talking about anything other than cost-of-living is a wasted minute in my book.”
The next major test for Sir Keir will come in May, when Labour are braced for najor losses in Sccottish, Welsh and English local elections.
However, with the prospect of a tricky Budget next week, there has been speculation a leadership challenge could come sooner.
Anyone mounting a leadership bid would need the backing of at least 80 Labour MPs.
Only a small number of Labour MPs have publicly called for Sir Keir to be replaced but many more have raised concerns about his leadership privately.
On Friday, Nottingham East MP Nadia Whittome, who is on the left of the party, joined Labour backbencher Clive Lewis in calling for a new leader.
“Even if Keir Starmer had a radical change of direction, I don’t think people would believe him. And I don’t think people around him would allow that to happen,” she said in an interview with former Labour candidate Ali Milani.
“So I think there has to be a change in leadership, a change in personnel, of the people in Number 10, and a completely different direction for the party.”
Earlier this week Rachael Maskell, who was recently readmitted to Labour’s parliamentary party after a four-month suspension for leading a rebellion over proposed welfare cuts, suggested the PM should consider his position if next week’s Budget does not deliver.
“Ultimately, the prime minister needs to look in the mirror and say ‘Do I have the skills at this particular time in our history to lead the Labour Party?’,” the Labour MP for York Central told LBC.
Challenged over her comments and whether he was the right man to lead the country, Sir Keir said he had proven his doubters wrong in the past by changing the Labour Party and winning a landslide election victory last year.
“Now people will say to me, ‘It’s not possible to change the country for the better.’ I say it is,” he told the BBC.
“I’m optimistic about the future of our country and I know that we can turn it around after 14 years of failure under the Conservatives.”
