There are many organisations with initiatives related to dark skies:
The International Dark-Sky Association (IDA) is the world authority on light pollution and is the leading organization combating light pollution to protect the night skies for present and future generations.
International Dark Sky Parks and Reserves are area's designated by the IDA for the quality of their night skies. The South Downs National Park has International Dark Sky Reserve status.
Dark Sky Discovery Sites are a nationwide network of places that provide great views of the night sky and which are accessible to everyone. In order to qualify for Dark Sky Discovery Site status, the locations need to meet a number of criteria that make them safe and accessible as well as having suitably dark skies.
A map of Dark Sky Discovery Sites can be viewed at: http://www.darkskydiscovery.org.uk/dark-sky-discovery-sites/map.html