Take for example the Boscastle flood. Something like seven Sea Kings used at the same time. Or the Fastnet race incident. How many were used there - something like 15 combined from Navy and RAF??
Don't forget there are about 100 RN Helos available to back up the civ SAR if required, all with SAR qualified crews. I accept that on any given day this number is not around but 10s could easily be generated at a reasonable notice for a major event.