Details of the UKRI guidance on sick leave (as well as annual leave) is available here (in particular, see TGC 8.2 and 8.3 on page 17 onwards of the document): https://www.ukri.org/wp-content/uploads/2025/10/UKRI-011025-StandardTrainingGrant-TermsandConditions.pdf.
University of Liverpool
Details regarding absences are available in the PGR handbook: (see page 29, Chapter 7: When Things Change). Also details of local support are available in your local institute PGR handbook.
University of Sheffield
Several details are available online:
Leave of absence information: https://www.sheffield.ac.uk/rpi/pgr/manage/leave-absence
Working, holidays and placements: https://www.sheffield.ac.uk/rpi/pgr/manage/working-and-holidays
General information for UKRI-funded students, including suspending studies: https://www.sheffield.ac.uk/rpi/pgr/scholarships/award-holders/information-ukri-scholarship-holders
University of York
Details regarding absences are on the YGR webpages: (for ill health see https://www.york.ac.uk/students/health/self-certification-illness/ and for holiday entitlement see https://www.york.ac.uk/research/graduate-school/support/).