Landers,
The UK CAA has just recently completed and published a complete review of North Sea helicopter operations, and safety thereof. It is available via the CAA website and what you are looking for is "CAP 1145".
I suggest you spend some time with this document in its entirety.
Don't be surprised if people are a little defensive in the forum about your subject matter interests, some are getting a bit tired of these ad hoc trawls, by un-credentialled individuals, for use in a document/publication they are unlikely to see, or be credited with, in supplying information.
The credibility of your own research, may well appear a little "sus" if you're just going to be basing it on snippets gleaned from a free-form, public access, internet forum.
Kind regards.
BS