If a mere civvie can comment....
I've long thought (as a keen mountaineer) that the RAF/RN have been a victim of their own success in respect of the SAR tasking - they provide such an efficient service that there is no need to provide a civillian rescue service in many areas of the country (It's noticable that in those areas without MIlSAR coverage, then you have the HMCG Helos).
There are a couple of other issues that may affect this - if a Civillian organisation takes over with civillian rescue as it's prime task, it may lead to an increase in demand for 'costs recovery' - ie get back from the rescued the costs of the rescue - and an need for insurance for those who require the services of the SAR.
Also, am I cynical in thinking that nay SAR purchase will be the S-92 as a sop to Sikorsky for the US101?