The Conservatives have increased their opinion poll lead over Labour to 19 points in the wake of Chancellor Philip Hammond's Spring Budget, figures released by YouGov on Friday (10 March) show.
The survey for The Times, conducted between 8 and 9 March, put the Tories on 44% (+2), Labour on 25% (unchanged), Ukip on 11% (-1) and the Liberal Democrats on 10% (-1).
The data will be a new blow to Jeremy Corbyn's leadership, with the left-winger vowing to stay on after Labour's historic defeat in the Copeland by-election in February.
The survey will also be a boost for Hammond as the government faces a backlash over his plan to scrap class two National Insurance Contributions (NICs) for self-employed workers from April 2018 and increase the main rate (class four) NICs from 9% to 10%, with an additional 1% hike in April 2019.
The reform has sparked controversy because the Conservatives promised not to increase income tax, VAT or National Insurance in their 2015 general election manifesto. Theresa May was forced to delay the hike as more than a dozen Tory MPs are expected to rebel against the move.
"We did make some difficult decisions in the Budget yesterday. Is it fair? I think it is fair to close the gap in contributions between two people doing the same work and using the same public services to make the same contribution to wider society," the prime minister told reporters in Brussels.
Leading independent think tank the Institute for Fiscal Studies (IFS) has described the reform as a "small step" in the right direction. But Labour's Shadow Chancellor John McDonnell has called on May and Hammond to scrap the planned hike.
"The fact the prime minister won't fully support her own Chancellor's Budget measure, and has been forced by Labour to row back on it just 24 hours after he delivered his speech in parliament, shows the level of disarray that exists at the top of government," McDonnell said.
"Labour have been clear from the moment they were announced that we will oppose these tax rises on low and middle earners, as we don't think it is a laughing matter, unlike May and Hammond. What is even more alarming is that the government didn't stop and think before announcing such a tax hike.
"It should have been obvious that they would need to consult first, or at least wait until after their review on self-employment had finish, before announcing such drastic changes. As a result millions of ordinary working families will have been made to worry, and will now be holding their breath until the Government makes up their mind," said McDonnell.
"May should simply show some leadership, rather than this partial U-turn, and just scrap these tax rises for low and middle earners altogether."