[Lapha]

Note that the author of the unauthorised derivative work 'B', based on the 'original' work 'A', still retains copyright over their own (unauthorised) work B. Even if a court compels the author of B to stop distributing their infringing work B this fact doesn't change, B doesn't go out of copyright, and the author of A (or anybody else for that matter) doesn't have any additional rights to the use the work B.

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.