Under British law (s11 of the Copyright, Designs and Patents Act 1988), the first copyright of a book belongs to its creator, or, if the creator writes it for an employer, his employer (s9). Now his employer does not have to be a natural person; it could be a fictitious legal person, such as a company. If it is, does the copyright expire and if so, when? S12 states that copyright endures until 70 years after the author dies. Does that mean that if a company holds the first copyright then the copyright lasts as long as the company stays in existence, plus 70 years? If so, what is to stop an author avoiding the automatic expiry of copyright 70 years after he dies by incorporating himself as a company for which he does the work of writing? Or perhaps a company that holds the first copyright loses it 70 years after its employee dies?
Regardless of whether the first copyright holder is the author (always a natural person) or an employer (natural or non-natural), the copyright under British law expires 70 years after the death of the author.
British law makes a distinction between the author of a work and the owner of a copyright that is not present in U.S. copyright law. This gives the author of the work "moral rights" which are absent in U.S. copyright law and also changes the analysis of how long a copyright lasts.
Under Section 9 of the law, the author of the work is always a natural person according to the rules set forth there, and if no natural person can be associated with the work, it is a work of unknown authorship.
Section 11 governs who owns a work, not who its author is, so the fact that a work is made for hire under a corporation does not mean that the author of the work is the corporation. Indeed, by definition, the author of the work cannot be a corporation. If no individual can be associated with a corporate work it is simply a work by an unknown author.
A work by an unknown author enters the public domain 70 years after it is created, or 70 years after publication if it is first published within 70 years after its creation, pursuant to Section 12.
The authorship of a work is fixed under Section 9 at the moment of its creation, so neither the first owner of the copyright (under Section 11) nor an assignment of ownership of the copyright from the author or first copyright owner to someone else (in your scenario where an author transfers ownership of the copyright to a corporation) changes the author of work. Hence, neither the fact that a work is made for hire, nor the fact that the author transfers ownership of the copyright, changes the duration of the copyright.