In order to establish if a piece of writing is in copyright, you need to know two things: the country in which the work was published, and how copyright law works in that country.
In the United Kingdom, as a general rule, work remains in copyright for seventy years following the end of the year in which the author died.
In order to quote from work which is still within copyright, then, you will need permission from the copyright holder. Yes? No!
The Copyright Act states that if quotations can be regarded as “fair dealing... for purposes of criticism or review”, then they can be used without permission, so long as both the author and title of the original publication are cited.
The Copyright Act, however, offers no clear or legal definition of “fair dealing”, so the Society of Authors and the Publishers Association have provided their own:
A single extract of up to 400 words or a series of extracts (of which none exceeds 300 words) to a total of 800 words from a prose work [or] extracts to a total of 40 lines from a poem, provided that this did not exceed a quarter of the poem.... the words MUST be quoted in the context or of “criticism or review”.
While that definition is not part of the Copyright Act, and so cannot be used as a legal definition, it has been accepted in Court as a useful guide—although not a definitive one.
If you are in any doubt then obtain permission before you quote, or don’t quote at all.