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/solvency2-internal-model-reporting-codes-and-components-ss

Related links

Solvency Capital Requirement - Internal Models
CP20/15 - Solvency II: internal model reporting codes and components and life product codes https://www.bankofengland.co.uk/prudential-regulation/publication/2015/solvency-2-internal-model-reporting-codes-and-components-and-life-product-codes