Policies set the strategy for managing development so that it is not done in a piecemeal way, but all contributes to the overall aims of the city, region or country. Policies have the greatest weight when decisions are made on whether a development should be permitted.
Planning policy can be national policy, set through Act of Parliament.
eg. the Town and Country Planning Act 1990, the Localism Act 2011, and the Growth and Infrastructure Act 2013. Full list here
Planning policy was largely superseded by the National Planning Policy Framework which was brought in in 2012 in an attempt to reduce the large quantity of policy guidance documents into a single document. See here
It can be regional policy.
The Regional Spatial Strategies RSS which set out polices to cover regions of the country, were scrapped by the Coalition government, but in Bristol the council works with neighbouring councils in the West of England Local Enterprise partnership (Bristol, North Somerset, South Gloucestershire and Bath and North East Somerset, BANES). The WoE LEP has a strategic framework of the 4 councils core strategies covering joint infrastructure requirements. Read more here
It is also Local Policy.
In Bristol the Core Strategy is the main policy document. The Sites Allocations document and Development Management Policies give more detailed policy and further documents are in production to set policy for development in the Central area of Bristol for instance. Read more here
Under the Localism Act 2011, a Neighbourhood Development Plan which has been passed at referendum also becomes neighbourhood policy.
Note that although policies have the greatest weight, they are still only part of the picture. Other ‘material considerations‘ may outweigh policies in the opinion of the case officer, the planning committee or the planning inspector who makes the final decision on whether to permit a particular planning application.
There are also supplementary guidance documents which do not have the same planning weight but are material considerations, such as the National Planning Policy Framework or local supplementary planning documents such as SPD 4 on Developer Contributions.