Whilst I have come this thread rather late - and must admit that I have trouble following some of the arguments - it surprises me that little has been said about the NATS licence.
The licence specifies the services that NATS must provide with, as I recall, some services given greater priority than others. The licence terms change over time - and I haven't been involved in stuff like this of late so I don't know what it currently says - but I wonder whether the service to SFR traffic features at all. Perhaps the licence, which is set by government, will give an indication of NATS' obligation to build in contingency for sickness etc. After all, as has been pointed out, government is a major shareholder!
As for Jim's rather simplistic approach of 'if you need more resources then get them' doesn't seem to work in ATC. It takes a significant period of time to train a controller and every one that gets through the training can probably be put to better use than handling SVFR two or three times over. Throwing money at the problem and putting more trainees through the system doesn't work for a variety of reasons. Perhaps the perennially high attrition rate in NATS ATC training could be reduced in some way - but I guess that's another can of worms.........