If I take the phone out of the case, the compass comes back to life but doesn't work, in that North might be anywhere. However a few compass recalibrations and it works. It seems to be the magnetic clasp on the case.
I used a case with my old GS3 that had a much stronger magnetic clasp and there was no trouble with the compass.
I'm disappointed that I've been sold a case that causes part of the phone to not work. Before I go back to the Vodafone store with this problem, does anyone have any comment?