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Is this just a difference due to British English vs American English?
Armagh, Banbridge and Craigavon Borough Council's grammatical error appeared on an advert for a performance of Charles Dickens' Great Expectations in July.
Strunk and White
Form the possessive singular of nouns with 's.
Follow this rule whatever the final consonant. Thus write,
Charles's friend Burns's poems the witch's malice
This is the usage of the United States Government Printing Office and of the Oxford University Press. Exceptions are the possessives of ancient proper names in -es and -is, the possessive Jesus', and such forms as for conscience' sake, for righteousness' sake. ...