In that neck of the woods, its most likely to have been a Royal Navy Seaking from Prestwick. Used to be 819 Sqn although I have a feeling they're part of 771 now - I stand to be corrected.
I think you'll find that, if it's the Navy, and therefore a Seaking, it will have been
grey & red - the white & red tend to be Coastguard / Bristows SAR S61s.
Flying from 200' to a 50' hover at night, over the water, is well within the capabilities of this greatest of submarine-chasing helicopters, now admirably still serving in the SAR role.
