In order to receive the full flat-rate state pension (currently £159.55 per week) you need to accrue 35 years of national insurance (NI) credits. It’s easy to find out how many NI credit years you already have: log in to your online personal tax account on gov.uk/personal-tax-account
If you contracted out of the state pension for any significant period in the past, your predicted state pension entitlement will be smaller, but the maximum pension can be obtained by paying NI for additional years.
Where you have already racked – up 35 full years of NI credits and your pension prediction says you qualify for the full pension, why would you pay more? You may want to protect your entitlement to unemployment support, maternity or sick pay, but if you work for yourself those state benefits are largely irrelevant.
Most directors of their own companies pay themselves just enough salary to get an NI credit, but don’t actually pay any NI. If you don’t need the NI credits, you could stop paying yourself a salary.