In reality we dont have "game officials" or anything like that regarding the UK whilst no one would be likely to care, Its always been my assumption this site were probably the individuals that are prone too police showing up too our doors (planned, or unplanned) whilst most probably have zero clue regarding the laws Its always been a "what if" scenario.
Weirdly enough if you come across any seal bones there totally legal to hold though with no licenses, only the cetaceans family require it.
But I had that thought with my bird of prey skulls that dont have a a10 license Its completely legal to keep them as a individual without it. (a10 just allows the sales, and gives each "product" an ID number plus proof of origin) But I always figured I would get rid of them when It comes time to apply for my FAC I could easy enough give them away to someone that would love them and go out and find a complete one and apply for the a10, or buy one that's perfect with an a10.
Cant have anyone complain when there's government proof of its origins, and legitimacy but same time I wouldn't blame someone for raising there eyebrow at someone that does country-side things with firearms having protected animal parts either.