@Silvaire1 - if we go back to basic principles ATC is there to provide the appropriate service to all airspace users and it is a State responsibility to to ensure that the requisite services are provided. Issues of who pays the bills and pritavisation of service providers may present challenges to well established practices but the fundamental principles remain sound and are embodied in the Chicago Convention).
I was not really intending to suggest that fare-paying passengers deserve a better level of protection than anyone in any other aircraft operating to the same rules and procedures but rather to illustrate the most common justification for establishing CAS.
Going back to the principles, the Chicago Convention places obligations on States (amongst other things) to put the aviation infrastructure in place. It is left to the States to determine how best to do this and, in most cases, rules are issued and a regulator is established to check that the rules are followed. Commercial pressures have been perceived or invented by today's privatised and semi-privatised service providers and have led to some believing that their services should only be made available to those who directly pay the bills. In an ideal world the regulator acts as a counterbalance and ensures that the relevant principles remain in effect.
Of course, the world changes and the way in which the regulator will have to do its job today will be very different in some ways to the way it worked 25 or 30 years ago. Unfortunately - and probably justifying their common reputations as dinosaurs - many working within the regulators (and often those at senior levels who set policy) have not worked in a service provider for many years and assume that the nothing has changed since they left.
Sir George hits on a large part of the problem in the UK in that two different parts of the CAA have responsibilities with respect to airspace and regulating it. From my experience these two departments work differently and don't see eye-to-eye on the way each other works and sometimes indulge in a bit of infighting and point-scoring at the expense of setting clear regulations for service providers. This is compounded by a lack of clear direction and control from Government/DfT who, certainly in the past, paid little care for ensuring compliance with international obligations etc. and more for getting the major service providers and airports sold off.
It would be nice to think that things will get better in the future as Europe 'takes over' but, sadly, the way things are going it looks to me like we will have similar problems with different agencies dealing with different parts of the system and the potential for some of the basics to slip between cracks.