The Higher Education Funding Council for England and three other UK funding bodies (the Scottish Funding Council, the Higher Education Funding Council for Wales and the Department for Employment and Learning) have enacted an open access mandate.
Here's an excerpt:
5. The core of this policy is as follows: to be eligible for submission to the post-2014 REF, outputs must have been deposited in an institutional or subject repository on acceptance for publication, and made open-access within a specified time period. This requirement applies to journal articles and conference proceedings only; monographs and other long-form publications, research data and creative and practice-based research outputs are out of scope. Only articles and proceedings accepted for publication after 1 April 2016 will need to fulfil these requirements, but we would strongly urge institutions to implement the policy now. The policy gives a further list of cases where outputs will not need to fulfil the requirements.