Here is a list of useful arts organisations for engaging with politics:
The Act for Change Project: http://www.act-for-change.com/
British Theatre Consortium: http://britishtheatreconference.co.uk/
Creative Industries Federation: http://www.creativeindustriesfederation.com/
Devoted and Disgruntled: http://www.devotedanddisgruntled.com/
Equity: https://www.equity.org.uk/home/
Fun Palaces: http://funpalaces.co.uk/
In Battalions: http://finkennedy.co.uk/In-Battalions
My Theatre Matters: http://www.mytheatrematters.com/
Rebalancing Our Cultural Capital: http://www.gpsculture.co.uk/index.php
The Warwick Commission: http://www2.warwick.ac.uk/research/warwickcommission/futureculture/
What Next: http://www.whatnextculture.co.uk/
The Writers Guild: https://writersguild.org.uk/