This SS has not yet been added to the PRA Rulebook. It is available on the Bank of England website, here.

https://www.bankofengland.co.uk/prudential-regulation/publication/2015/the-pras-approach-to-supervising-liquidity-and-funding-risks-ss

Related links

Internal Liquidity Adequacy Assessment
Liquidity Coverage Requirement - UK Designated Investment Firms
PS15/23 - The Strong and Simple Framework: Scope Criteria, Liquidity and Disclosure Requirements https://www.bankofengland.co.uk/prudential-regulation/publication/2023/december/strong-and-simple-framework-policy-statement