It will hit the self-employed and those who take out individual policies disproportionately hard, according to the Association of British Insurers, because they pay the Insurance Premium Tax themselves, whereas companies pay the tax for employees who are part of a group scheme.

Mr Corbyn described the car parking fees as "a tax on serious illness" but it would mean yet another tax rise under Labour for millions of middle income families.

Around 10 per cent of the population has private medical cover, meaning the policy would affect six million people, though the figure includes children and spouses who are covered on family policies.