When tackling essays foreign approaches are great - they can show why the home approach is unacceptable, may need some reform in the interests of universal justice etc. As for Halsbury's I have no idea, but judges do cite it.. and if a judge cites it, why shouldn't you?
As for in problem questions you shouldn't discuss alternative legal approaches where the english aproach is dead clear, unless the question asks you to critically evaluate the law aswell (we get this element in most of our problem questions, dunno if anyone else does). I sometimes find that if you have time throwing some sort of critical comment in doesn't do your grade any harm regardless, but only as an extra... don't sacrifice on addressing the question for this.