You need to include the following:
Author(s). Title of report. [Internet] if online. Place of publication, publisher; year of publication [cited year month day] if online. Pagination. Report series and number (if available). Available from: URL or DOI.
NICE Guideline:
National Institute for Health and Care Excellence. Safeguarding adults in care homes. [Internet]. London, NICE, 2021 [cited 2021 Mar 1]. 102 p. [NG194]. Available from: http://www.nice.org.uk/guidance/ng189.
Selecting the PDF version will give you the number of pages of the report.