In general, Wikipedia has a good list of different countries' copyright term lengths. The longest term is 99 years after the author's death, offered in the Ivory Coast. (Mexico offers 100 years after the author's death, but only for works published after 2003.)

However, Great Britain has made several exceptions to its general copyright laws for specific works. The oldest two works currently under copyright are the King James Bible and the Book of Common Prayer; copyright in both of them will continue to be held by the Crown until 2039. (See Schedule 1 part 13(1) of the Copyright, Designs and Patents Act 1988.)