I know of a fair number of RN Sea King pilots who left the Service to fly for BA, but I think most of them did so however via a spell flying the Jetstreams at Culdrose. Although one at least did go straight from rotary to an airline job. I'll try to get the story of how he did that and what credits he received from CAA FCL.
I recall that at the time, BA regarded their multi-crew Sea King experience as highly desirable, maybe to the chagrin of some fast-jet pilots going for the same job!! However, this was perhaps a "phase" and the emphasis on employability may have now have change in nature.
The only further advice is to email CAA FCL and explain EXACTLY what flying experience you have and asking them to define EXACTLY what fixed wing hours you require. No matter which Flight Training Organisation you approach they will all say - "show me what you have in writing from CAA FCL" so you might as well clarify it with them NOW.
You are right, LASORS is open to a degree of interpretation when trying to delve into Military credits. No point trying to second guess and (perhaps) raising your hopes - ASK the CAA and obtain your own personalised "ruling".
Good luck
