Do students have the right to discuss exam difficulty,object to results or challenge the marks?

To my mind NO!  In the politically correct world that we live in I think that we sometimes question things for the sake of being seen to be correct rather than accepting that some of the "old methods" are actually right. Certainly in cases where there appears to a "trend" of things not being quite right, then this can be questioned, investigated and remedial action taken, if applicable, but don't do it just for the sake of appearing to be politically correct!