Two thoughts in particular about Fred's comments above.
(1) The moment you have two providers in the same bit of airspace, you have a potential problem. It really shouldn't be hard in Britain to have a line on the chart, that clearly demarks to whom an aircraft should be talking, where (and if necessary, when).
(2) Historically instrument approaches are primarily controlled by a pilot, with supporting information from controllers. Historically pilots are also responsible for see-and-avoid in VMC. Always and forever, pilots are responsible for the safety of their aircraft. Therefore, particularly since this technology exists and is becoming increasingly affordable, I think that future collision avoidance strategies should concentrate on putting information directly into the cockpit - not be reliant on information from a controller [notwithstanding that I'd still like to see (1) sorted out in British airspace].
G