It is estimated that the change will cost those affected an average of an additional 60p per week.
But Mrs May insisted that Mr Hammond's planned 2% hike in Class 4 NICs for the self-employed was "fair", when considered in the light of the abolition of the separate Class 2 payments as well as improvements to the benefits received by self-employed people.
If you are self-employed the amount of National Insurance you pay is going to rise from April 2018.
"The Conservatives have broken a clear manifesto pledge".
Theresa May has been accused of a partial U-turn in the face of a potential Tory revolt over the Budget's controversial National Insurance hike.
David Cameron also said in speech in December 2015: "We said in our manifesto we would not raise VAT, National Insurance or income tax for the next five years".
Dominic Raab, a former minister, said: "I struggle with the changes to national insurance for the self-employed".
Instead, the Chancellor told the Commons on Wednesday he would increase the 9% levy on the profits of self-employed people to 10% next year and then 11% in 2019, raising an extra £2 billion in tax revenue.
"Historically, the differences in NICs [National Insurance Contributions] between those in employment and the self-employed reflected differences in state pensions and contributory welfare benefits".
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Hammond allocated £2 billion for adult social care over the next three years, but the Jewish charities said the Government needed to go further and announce plans to secure long-term funding.
"When we spoke to South West business leaders at a recent series of events, more than three-quarters said that lack of infrastructure investment is holding the region back".
Hollands said the "aggressive" cut was clearly aimed at employees and directors of small businesses who might remunerate themselves partly or wholly through dividends rather than salary.
Speaking in Brussels, May defended the policy, and pointed to the independent think-tank, the Institute of Fiscal Studies, support for the change.
Mr Hammond, concerned by the threat to tax revenues by the growing trend towards self-employment, said the move was driven by a need to eliminate unfairness in the tax system.
As such, Hammond means to raise class 4 NICs by one per cent to ten per cent from April 2018.
The gap in tax paid by self-employed workers and the traditional employee has always been emphasised - something that led Hammond to believe the rapid rise in self-employment figures had little to do with entrepreneurialism.