The short answer
In the UK, copyright in a literary, dramatic, musical or artistic work lasts for the author's life plus 70 years, counted to the end of the calendar year of death. Film copyright lasts 70 years from the end of the year in which the last of four key people died: the principal director, the screenwriter, the author of the dialogue and the composer of music written for the film.
Books, plays and music
Under the Copyright, Designs and Patents Act 1988, the term for a literary, dramatic, musical or artistic work is the life of the author plus 70 years. The count runs to the end of the calendar year in which the author died, so the work becomes free on the following 1 January.
For joint authors, the 70 years run from the death of the last to die. Where the author is unknown, copyright lasts 70 years from when the work was made, or from when it was first made available to the public.
Films
A film's copyright runs for 70 years from the end of the year in which the last of these people died: the principal director, the author of the screenplay, the author of the dialogue, and the composer of music specially created for the film. A film can therefore stay in copyright long after its release, and the underlying novel may have a different date altogether.
Published editions
The publisher of an edition has a separate, shorter right in its typographical arrangement: 25 years from the end of the year of publication. It protects the layout of the page, not the words, so it seldom matters to an adaptation, but it does mean you should not photocopy a recent edition of an old text as your source.
Unpublished works
A transitional rule keeps some unpublished works in copyright until the end of 2039: works by authors who died before 1969 that had not been published by 1989. Letters, diaries and manuscripts are the usual examples, and they matter to true stories built on private papers.
The UK and the EU
The EU term is the same, life plus 70, with the same rule for films. A work out of copyright in the UK is usually out of copyright across the EU too, though national transitional rules can differ at the edges.
Questions
On 1 January after the 70th anniversary of the author's death. An author who died in 1955 is out of copyright from 1 January 2026.
70 years from the end of the year in which the last of the principal director, screenwriter, dialogue author or composer of the film's original music died.
The term is the same, life plus 70, with the same film rule, so dates usually match. Transitional rules can differ for some older works.