This is false. It's possible for both you and the original author to simultaneously infringe each other's copyrights. This is unintuitive but true due to the simple fact that you own all the original parts of your work.
In this particular case the Guardian article doesn't answer the question, but it's almost certainly the case that the courts found that Tolkien's estate didn't infringe upon Polychron's unauthorised work. In the UK (and much of the world), the bar for creating an original work is incredibly low, currently it's the EU approach where the author needs to express (creative) originality through choice, selection, or arrangement of a work. Previously the UK had the 'sweat of the brow' rule where the bar was even lower, only requiring 'labour, skill or judgement' in producing a work. The UK also explicitly protects derivative works from being considered infringement if they're found to be a parody, caricature, or pastiche, but this obviously isn't the case here.
Also note that 'copyright service' is a private company that sells copyright protection as a service through registering a work. The UK, unlike some countries, has no register of copyrighted works so you don't need to register a work for it to receive copyright protection in the UK.
Japan's very lucrative doujinshi (read: fan novels) and fan art scenes exist purely because most of the creators and publishers turn a blind eye to them (it's free marketing and good will from fans of their works). They only start caring if the fan works are being sold for profit or harming the original IPs.
Comiket exists thanks to everyone knowing and respecting where the invisible lines in the sand are drawn.
Permission is absolutely required in Japan, legally speaking. In practice, the requirement for permission is ignored under gentlemen's agreements.
I'm honestly asking because I can't find anything that goes as far as the claim you're making regarding original elements. I'm not even sure what original/severable elements could exist in that particular case.
“We need not pursue the issue of originality of derivative works. The Copyright Act grants the owner of a copyright the exclusive right to prepare derivative works based upon the copyrighted work. […] So Pickett could not make a derivative work based on the Prince symbol without Prince's authorization even if Pickett's guitar had a smidgeon of originality.”