Not an easy thing to explain. The UK, unlike just about every other State, has always allowed an air traffic control service to be provided outside CAS - in some ways it even encourages it. As a result, it has had to invent rules and procedures to deal with the anomalies that are created.
The usual reason or justification offered is that the UK is a relatively small place and the establishment of CAS limits mil and GA activity - it's certainly true that the mil and GA lobby are the traditional opponents of any extension to the CAS system (joined more recently by the green lobby).
Given the difficulty in establishing CAS where it is justified to provide the appropriate protection to commercial GAT, the prevalence of control services being provided outside controlled airspace (in many areas) has increased over time.
Although it doesn't help a great deal, you are not alone - there are a good many UK pilots (and a few controllers) who don't understand the implication of the rules and services that apply outside CAS!
Last edited by Spitoon; 9th Jan 2011 at 18:13.
Reason: spilling