Philip Hammond made a “rookie error” in the Budget, Conservative former Chancellor Norman Lamont has said.
Lord Lamont criticised the planned rise in National Insurance for self-employed workers, a policy that breaks explicit pledges made in the Tory manifesto.
The peer, who served as Chancellor between 1990 until 1993, said it was fortunate for Mr Hammond that there was no general election looming and that he had time to regain trust.
Self-employed workers will see their rate rise from 9 per cent to 10 per cent in 2018, with a further rise to 11 per cent in 2019. The Treasury expects 2.5 million people to be hit.
“Election pledges should not be lightly given ... tax pledges cannot be lightly cast aside,” Lord Lamont wrote in an article for the Daily Telegraph.
“My guess is that, in time, the Chancellor's tax raid on the self-employed will be seen as a rookie error.
“He is fortunate in having plenty of time to regain trust on tax before the next election.”
The Chancellor justified the policy on the basis that differences in benefits between employees and self-employed workers “have been very substantially reduced” in recent years.
The plan has been backed by the respected Institute for Fiscal Studies, which says it will remove distortions in the tax system.
Over a dozen Conservative MPs have, however, publicly come out against the tax rise, with a rebellion possible.