Keir Starmer said he had no "magic wand" to fix Britain's problems after three opinion polls put his opposition Labour Party on track for a historic election landslide on July 4.
The Labour leader is set to walk into the prime minister's office at 10 Downing Street with a 200-seat majority, the biggest for any party for a century, according to the latest poll by YouGov.
It suggests Labour will win 425 parliamentary seats, while Prime Minister Rishi Sunak's Conservatives will slump to 108, down from the 365 they won at the last election in 2019, with a swathe of senior ministers expected to lose their seats.
A Savanta poll for the Telegraph put Labour on 516 seats and the Conservatives on just 53, a wipeout that would see Sunak become the first British prime minister in history to lose his own seat in a national election.
Many voters have told pollsters their main motivation is to get rid of the Conservatives, in power for 14 years during a period of political and economic turmoil.
Starmer, who has pledged not to raise the main taxes paid by working people, has sought to push back on any suggestion that a Labour government could have an immediate big impact on issues like the cost of living and standard of public services.
"There's no magic wand that we can wave the day after the election and fix all the country's problems. And nobody would believe us if we said there is," he told ITV's Peston programme.
He said his focus would be on expanding the economy rather than on increasing taxes.
"If all you do is tax the existing pie or cut the spending of the existing pie, which is ever-reducing, you are going round and round in circles," he said.
Sunak's Conservatives have sought to turn the spotlight onto tax, saying a Labour government would cost households more.
However, the tax bill is already at a 70-year high and will continue to rise even if the Conservatives win because both parties have pledged to freeze tax thresholds.
Conservative heavyweight Michael Gove, who is standing down at the election, said the poll that mattered was on July 4.
"You can look at the opinion polls ... but this election is not an election between Savanta and YouGov, it is between Keir Starmer and Rishi Sunak, and there's therefore a choice of policies."
Sunak, Starmer and other leaders will face questions from an audience of voters on the BBC later on Thursday.
