The NMC Standards of Proficiency can be referenced as webpages, following the example in the Harvard referencing guide Cite them Right.
This document has page numbers, so the relevant page number should be included in your citation when you are directly quoting or paraphrasing. You can also mention specific sections to clearly signpost the reader/assessor.
Nursing & Midwifery Council (2024) Standards of Proficiency for Registered Nurses.