Bit of thread drift perhaps, but...........
In addition to an ATS provider having to justify the safety of its procedures, the local ATC procedures are considered by some companies to represent valuable intellectual property.
NATS is not the only ATC service provider at UK airports - I think in total there are something in the region of 40 to 50 separate prover orgnisations. Many airports will contract out the ATC service provision and one of the things that makes it harder for a new provider to bid is not having access to the existing local procedures (and therefore taking time and effort to develop them. Of course they don't have time to do this when they take over a contract, the airport will want the service provided on day 1. Hence although on paper it is an open and competitive market, in reality it is a generally static market with very little change over of service provider.
The intellectual property rights of local procedures were not really an issue before the privatisation of NATS but have since become keenly protected. Maybe this is just a change in the general view on IPR or maybe it is something that NATS made an issue of in the ATS business - doesn't really matter I guess.....
Although it is primarily a commercial matter it is sad to see that this form of protectionism has been permitted by the CAA. Historically the CAA has typically steered well clear of anything that can be vaugely considered commercial but there are some safety issues bound up in all of this as well.