If your pension provider that administers your pension goes out of business, the compensation you’re entitled to will be determined by the type of pension you have. It will also depend on whether your provider’s regulated by the Financial Conduct Authority (FCA)
For a defined contribution pension, if it qualifies as a ‘contract of long-term insurance’ it will be 100% covered by the Financial Services Compensation Scheme (FSCS). Annuities purchased from providers regulated by the FCA are also eligible for that same protection.
For any other pension types, any protection you have will depend on the underlying investment. You can see the full list of the different levels of compensation you’re entitled to from the FSCS here, and if you have any questions about your specific pension you should speak to your provider.