have you read the definition of controlled airspace in Schedule 1 to the The Air Navigation Order 2016? It says: ""Controlled airspace” means airspace which has been notified as Class A airspace, Class B airspace, Class C airspace, Class D airspace, Class E airspace, Class F airspace or Class G airspace;"
As it often does the ANO is contradicting itself and talking bollox, if Class G was controlled airspace then how on earth (or above it) could you have an ATSOCAS?
In the UK there are currently five classes of airspace; A,C,D,E and G. The classification of the airspace within a FIR determines the flight rules which apply and the minimum air traffic services which are to be provided. Classes A, C, D and E are areas of controlled airspace and G is uncontrolled airspace.