SOSL - the world wide CSAR cover has been looked at here already and is subject to totally different provisions. My understanding is the SAR force in the UK was not part of those arrangements.
As for cover to UK mil, touchwood, but the number of incidents involving UK mil ditching are vastly lower now than at any time in the past. It is the case that something like 97-99% of all call outs are civilian related.
The bravery of the SAR crews has been beyond question, but ultimately SAR has become an emergency service like the other blue light responders. Frankly at a time when money is tight, I'd rather MOD money was spent on equipment used on ops and not providing an emergency service that can be done, and has been done, with equal effectivness and courage by civilians for over 30 years.