IO540, thanks for your concise and precise answer, all of which I totally agree with.
On further reflection and with the benefit of having read your reply, I am now convinced that publishing the GUND and lat-lon values in this way is at best unnecessary clutter on the charts and at worst confusing and an encouragement to unsafe practices. I am all in favour of GPS navigation (used in the right way) but why on earth would the CAA want to do anything to encourage people to use cheap uncertified units without suitable databases for vertical navigation?
I'll write to the CAA and see what they have to say. I'll let you know if I get an answer.