The CAA already produce a list of 'Organisations Conducting CAA and JAR-FCL Approved Courses of Flight and Ground Training':
Standards Document 31 Version 106: Organisations Conducting CAA and JAR-FCL Approved Courses of Flight and Ground Training - Interim Document | Publications | About the CAA
For rotary providers, you will need Part 1 & Part 4. This document, however, does not include those organisations that only provide PPL(H) training.