Hallam made submissions to 14 units of assessment for REF2021. The impact case studies are available here.
One of the best things you can do to understand how REF impact case studies are assessed within your discipline is to read impact case studies from previous REFs. UKRI maintains searchable databases of all impact case studies submitted to both REF2014 and REF2021.
REF impact case studies are given a star rating, from unclassified up to 4*. These individual case study ratings are not given on the REF2014 database, but impact consultant Stephen Kemp has published a handy list of 4* impact case studies by unit of assessment.
Alternatively, you can look at the whole REF2014 ICS database.
The REF2014 ICS database has an excellent research functionality, which searches within each ICS for results.
You can also search for ICSs by unit of assessment, or by institution.
The star rating for individual impact case studies is not available, however you can make an educated guess by looking at the grade profile of the impact for the submitting unit.
To do this, go to the Results and submissions page, view the results by institution, click on the unit you’re interested in (e.g. 03 Health, 05 Biological Sciences, etc.) and look along the Impact line of the results graph.
You can’t tell for certain which ICSs scored which ratings (unless there is a 100% against one of the star ratings) – the grade profile reflects all the ICSs submitted by that unit, and in 2014 it included the score for the impact environment template (20% of the impact grade profile). But you can get a general idea.