This SoP 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/2018/pillar-2-liquidity

Related links

PS13/19 - Pillar 2 liquidity: Updates to the framework https://www.bankofengland.co.uk/prudential-regulation/publication/2019/pillar-2-liquidity-updates-to-the-framework