National Insurance is a tax paid by workers and the self-employed who are over 16, with the amount varying depending on how much you earn.
Employers do make some contributions on behalf of their workers, but it again depends on how much they are paid.
For employees, it is taken straight out of your salary before you receive it, while self-employed people need to pay as part of their self-assessment.
By paying the tax, you are entitled to a number of benefits, such as a state pension, Jobseeker’s Allowance and maternity pay.
The contributions cover these benefits, with some also going towards the NHS.
Where do the other parties stand on National Insurance?
The Liberal Democrats announced in their manifesto earlier that they plan to review the tax and National Insurance status of employees, dependent contractors and freelancers “to ensure fair and comparable treatment” and to “modernise rights to make them fit for the age of the gig economy”.
The Green Party also pledged in their manifesto – launched earlier this week – that they wanted to merge employees’ National Insurance, capital gains tax, inheritance tax, dividend tax and income tax into a single consolidated income tax, claiming it would “close loopholes” and bring in an additional £20bn to the public purse.
Labour has yet to publish its manifesto, but in an announcement about its plans for the “Living Wage” earlier this month, the party pledged not to raise income tax or National Insurance contributions for the bottom 95% of earners.
The SNP says on its website it would oppose any increases in National Insurance.