It will not take effect from July to allow payroll computer systems to be updated in time. It means everyone will temporarily start paying more every month in April when the planned NI rise comes in, before the threshold increase takes effect. 

Someone earning £30,000 a year currently pays £204.25 a month in NI. From April they will pay £222.15 a month, but will start paying £192.46 in July. However, employees earning £100,000 a year currently pay £489.90 a month in NI. From April, this will go up to £580.65 before falling slightly to £548.71 in July.

The 31 per cent increase in the starting threshold for paying NI was bigger than had been suggested in the run-up to the Spring Statement. However, wage inflation will drag more lower paid employees into the NI net over the next four years, said Shaun Moore, a  tax and financial planning expert at Quilter.

He warned that it would create administrative problems for employers, who would have to start the tax year with one set of assumptions for NI calculations and then change them from July.

Helen Morrissey, a senior pensions and retirement analyst at Hargreaves Lansdown, said: “By lifting the threshold, care must be taken that workers earning less than £12,570 per year do not lose access to vital NI credits for state pension.”