Despite the controversial move, ministers appeared to say that the NIC changes would go ahead.
The Office of Budget Responsibility (OBR), the official independent statistics body, expects the economy to be the same size in 2021 as before, but the growth will be better in the near-term, and worse later on.
The move has now been delayed until autumn, while May said Hammond would listen to concerns over the change.
But Mrs May said the proposals would make National Insurance "simpler, fairer and more progressive".
The tax has also been portrayed as a tax hit to the "white man van".
As a result of the decision self-employed workers paying the main rate of class 4 National Insurance contributions would see an increase by one per cent to 10 per cent in April 2018.
What has been so damaging is not so much the staged 2 per cent rise in contributions as the strong hint that he is considering going far further and equalising, as he sees it, the NI contributions of employed and the self-employed in the name of "fairness".
The abolition of Class 2 NICs by Mr Hammond's predecessor George Osborne in the 2016 Budget had been due to save 3.4 million people an average £134.
Tackling traffic menace top priority of new BMC Mayor
In the elections that concluded last month, the Shiv Sena won 84 of the 227 seats, while the BJP finished a close second with 82. On the political front, he will have to face an aggressive BJP, which has just two members less than Sena in the civic house.
Speaking to Sky News, Mr Hammond said the move would make the system fairer considering that employees and self-employed workers have access to similar benefits from the state.
Prime Minister Theresa May was forced to defend the National Insurance change after it sparked a backlash from Conservative MPs such as Iain Duncan Smith, John Redwood, Anna Soubry and Dominic Raab. That is not fair to the 85% of workers who are employees.
Tom Watson has called for the Government to ditch its National Insurance hike for self-employed workers as he accused the Prime Minister of breaking a Tory manifesto pledge.
The rebellion by Tory backbenchers over the changes has grown to about 20 MPs.
Liberal Democrat Treasury spokeswoman Baroness Kramer said: "This is a tax on builders, taxi drivers and window cleaners, some of Britain's hardest working people".
"Of course, the change to National Insurance will require legislation on its own, it won't be part of the finance bill, that's always what happens with National Insurance changes and those elements of the package will be brought forward in the autumn", May told reporters at the European Council summit in Brussels.
But Lamont said that he feared that Hammond's announcement, which breaks a Conservative election manifesto pledge, was a "rookie error".
Half are director-shareholders who have incorporated themselves as companies, but the others include savers with holdings of more than £50,000 in stocks and shares outside ISA schemes.