European Copyright Law: Council Directive 93/98/EEC of 29 October 1993 harmonizing the term of protection of copyright and certain related rights, article 1.1.
There we find that the rights of an author of a literary or artistic work within the meaning of Article 2 of the Berne Convention shall run for the life of the author and for 70 years after his death, irrespective of the date when the work is lawfully made available to the public.
David Cormack, writer of the excellent article on William Ashton Ellis, was kind enough to provide me with the following copyright related information:
In his will of 23 May 1918, Ellis bequeathed "the whole stock of my published literary works as standing in my name and to my credit at my printers and publishers at the time of my death together with my copyright and other legal rights therein" to "my valued friend Thomas Francis Howell [,] Barrister at law". Howell was also, together with Ellis's brother Sir Evelyn Campbell Ellis, executor of the will.
Howell asserted the inherited copyright at least once, as indicated by a slip bound into my copy L Archier Leroy's Wagner's Music Drama of the Ring, published by Noel Douglas, 38 Great Ormond Street, London WC1, no publication date, but the author's preface and H R Barbor's Introduction are both dated 1925. The slip reads:NOTICE
The quotations from Wagner's Essay, "Die Wibelungen," used in Chapter 2, are all taken from Vol.7 of "Richard Wagner's Prose Works," translated by William Ashton Ellis.
The copyright in this translation and in all other published literary works of the late Mr. Ellis is vested in T. Francis Howell, Esq., of 19, Phillimore Gardens, W.8, whose kind permission to reproduce the above-mentioned quotations is hereby acknowledged.
I have not come across any other assertions of copyright by Howell or his heirs or anyone else, nor have I been able to track down Howell, but perhaps the 70 year protection period should at least be regarded as running from 1925 rather than 1919.