The government has been urged to reconsider plans to increase taxes on the self-employed by the Kent MP Tom Tugendhat.

Chancellor Philip Hammond is facing claims the government has broken a manifesto pledge not to increase National Insurance contributions for the self-employed.

The measure, announced in the budget, has drawn criticism from several backbench Conservative MPs.

Mr Tugendhat, who represents Tonbridge and Malling, said: “I urge a rethink. We should be encouraging the self-employed, start-ups and people who are taking risks and carrying those risks themselves.

“We should recognise that through support, yes, but we should do so particularly through taxation.”

Mr Hammond has strongly defended the measure, saying that it is an issue of fairness.

The rise - set to add £240 a year to the payments of some 2.5 million self-employed people - has overshadowed the budget’s other key announcements, notably on social care and free schools.

Independent finance experts have backed the move, with the Institute for Fiscal Studies (IFS) saying the tax system needed reform and the measure was a step in the right direction.

Jo James, chief executive of Kent Invicta Chamber of Commerce, said: “Many entrepreneurs and sole traders will be disappointed to see significant rises to their national insurance bills over the coming years.

“Ministers need to ensure that these business people, who make a significant contribution to the economy, also get the recognition and benefits that correspond to their contribution.”