Theresa May has backed Philip Hammond's controversial National Insurance changes, but bowed to rebel Tory MPs by retreating on when they will be introduced.
Instead of being included in the Finance Bill, which implements the Budget, they will be brought in as part of separate legislation in the autumn, the Prime Minister announced.
And in a concession to her backbenchers, she pledged that her embattled Chancellor would speak to them about their concerns and publish a paper explaining the proposals before they are introduced.
Labour claimed the Prime Minister's move - which effectively puts the brakes on the Chancellor's Budget proposals - was a "partial U-turn" and said she was rowing back on Philip Hammond's plans.
But speaking in Brussels as a Tory mutiny over the plans appeared to be growing almost by the hour, she said the proposals would make National Insurance "simpler, fairer and more progressive".
Mrs May said the Chancellor's paper would contain details about reforms "along with some changes we plan to make on rights and protections for self-employed workers, including on issues like pension rights and parental rights and maternity pay".
She added: "The decision on National Insurance was taken in the context of a rapidly changing labour market in which the number of people in self-employment - often doing the same work as people employed more traditionally - is rising rapidly."
The Prime Minister also said the shift towards self-employment was "eroding the tax base" and making it harder to pay for public services "on which ordinary working families depend".
She said the National Insurance changes go "some way towards fixing that".
Responding to Mrs May's move to leave the door open to more concessions to her rebel MPs, shadow chancellor John McDonnell called on her to show leadership and scrap the proposals.
"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," he said.
"What is even more alarming is that the Government didn't stop and think before announcing such a tax hike."
The Prime Minister's comments came as a rebellion by Tory backbenchers over the changes grew to about 20 MPs, including one junior minister who called on the Chancellor to apologise for the increase.
Dissent is not just confined to backbenchers. Welsh Office junior minister Guto Bebb could be facing the sack for declaring in a radio interview: "I think we should apologise."
And he added: "I will apologise to every voter in Wales that read the Conservative manifesto in the 2015 election."
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