Apostrophes

[SteveD]

I normally have no problem with use of the apostrophe but I am involved in a discussion on another forum and am having a mental block about this:

Taking it for granted that there is more than one magistrate, which is correct, A, B or both ?:

A
Magistrates' Court

B
Magistrates Court

(The argument for B being that there is no possession; the magistrates do not own the court, it is a court FOR magistrates).

[factor-fiction]

My impression is that in the main the Yanks are actually much better at grammar and punctuation than we are in the UK.