alphaalpha,
I am current at Luton and Essex/Stansted and my reply to your comments would be;
I will always keep IFR traffic inside the lateral limits of CAS but it is not always possible to keep within two miles of the boundary. Luton and Stansted have similar problems as the example given by ATCO Two.
I never descend to less that 500 feet from the base of CAS but we routinely descend to the lowest available altitude above the base of Class A or D CAS. In the example given by TC_LTN, if you didn’t descend to 3000 feet on a base leg in the CTA then the inbound would be above the G/P. On 05 at Stansted you use 2000 feet in the CTA on the extended centreline for similar reasons and also sometimes to provide separation from following traffic if you are doing tight spacing.
If you contact me and advise me of a route which keeps you outside CAS then it will make no difference to my handling of IFR because, as already stated, you are deemed separated from traffic inside CAS and I will make sure that my IFR traffic stays inside. In some specific circumstances I may provide traffic information to IFR traffic inside CAS on traffic outside CAS but this is rare. Very occasionally IFR traffic will request information on traffic close to CAS if they have received a TCAS TA but most of the operators appear to understand the airspace around both airports.
If you request and are granted a VFR transit clearance then there is no requirement to provide standard separation, traffic information and/or traffic avoidance is all that is required. We routinely descend to 500 or 600 feet above operations inside CAS which are not in contact with us, for example the gliders at Halton and Dunstable if your doing Luton and the gliders at Hunsdon, North Weald and Weathersfield at Stansted.
In my opinion, if we were ever in the situation where we are required to keep IFR traffic inside CAS 1000 feet above traffic underneath CAS then the altitudes used inside CAS would stay the same and the base of CAS would be lowered. It would be difficult for a lot of departures from Luton, Stansted and, I would guess, London City to reach 1000 feet above the base of CAS and still comply with minimum noise routeings and noise abatement measures at the airports. It would also affect the altitudes used for arriving traffic and limit the amount of permissible operations within CAS such as gliding.
I understand the points made by the Duke and Bern Oulli regarding RAS but I haven’t had experience of providing RAS since we have been able to vector under RIS.