HEFCE has published a guide to the Research Excellence Framework (REF), reports ResearchResearch.com:

HEFCE – REF Guide (PDF)

The guide is a general introduction to the REF, the successor of the RAE, including details on how bibliometrics (citation data) will work. The pilot and consultation are ongoing, so the document does not go into the specifics of the system, but it does provide enough information for interested parties to develop a good overall impression of the proposed new method of research assessment.