It is an anonymous work or pseudonymous work and 50 years have passed since the date of its publication
It is another kind of work, and 50 years have passed since the year of death of the author (or last-surviving author)
It is work not published during the lifetime of the author, and 75 years have passed since the death of the author, or 50 years have passed since the date of its publication, whichever period is the shorter
It is a photographic work, sound recording, cinematograph film, television or sound broadcast and 50 years have passed since the date of its creation
It is a "original literary, dramatic, musical, or artistic work made by or under the direction or control of Her Majesty or a Government Department", and 50 years have passed since the date of its creation