After a disheartening day on Monday, yesterday took a turn for the better and ktelontour started to make progress. First port of call was the Nationwide to discuss my concerns and fully expecting more of the same bollocks, I was more than surprised at the reception.
I was seen immediately and told that after much effort (over three hours on the telephone apparently) they could now guarantee that we no longer be receiving any paper correspondence again (as we had before anyway) and they apologised profusely for their error.
No point flogging a dead horse (despite their claim it was a "legal" requirement, which I took issue over) and so I thanked them for their resolution and left them too it. In and out in under 10 minutes and everything back to normal.
So much for "just leave it as they don't listen". It seems they do if you are determined enough. :o)