Public Policy Impact is an important part of research impact. There are a number of ways in which research can achieve policy impact and resources available to assist researchers.
To look at examples of existing research impact, you can now view the REF2014 impact case studies at: http://results.ref.ac.uk/
Research by Cambridge academics feature in policy reports. One of the ways research has impact on public policy is through evidence to parliamentary committees. Many Cambridge academics provide expert evidence to select committees.
See the following report for a review of the role of select committees: http://www.ucl.ac.uk/constitution-unit/publications/tabs/unit-publications/153.pdf
See also the following report on the value of history to policy making: http://www.instituteforgovernment.org.uk
There are web-based resources to identify calls for parliamentary evidence in your research area. For example, Manchester University produce a regular list of calls for parliamentary evidence: http://www.policy.manchester.ac.uk/resources/evidence/
The Parliamentary Office for Science and Technology (POST) produce evidence summaries 'POST notes' on different topics: http://www.parliament.uk/mps-lords-and-offices/offices/bicameral/post/publications/)
POST has also recently established a social science section to boost social science evidence for parliamentarians:
http://blogs.lse.ac.uk/impactofsocialsciences/2013/09/09/exclusive-look-post-social-science-section/
‘Constituency Explorer’ is a new collaboration between the House of Commons Library and Durham University to provide information, evidence and links for constituencies: http://www.constituencyexplorer.org.uk/
See also the following website for evidence to select committees and alerts in your subject are: http://www.theyworkforyou.com/