OK I have taken this one step further and think I now realise what is going on.
My laptop uses an SiS671 chipset. The driver has never been bundled into Linux and over the years has always relied on 3rd party contributors to manage the video.
When I transitioned from "Linux Mint" to LMDE I continued successfully with the solution at the post here http://forums.linuxmint.com/viewtopic.php?f=59&t=54129
I now appears that if I install the respin and then update it the solution no longer works and xserver / gdm doesn't appear to work and LMDE drops to a command prompt at the point it would usually run xserver.
The only solution is to remove xorg.conf provided as a part of the solution which allows x to run but only in 800x600 resolution.
Can anybody suggest anyway to get around this? It's not really an option to say don't update as I guess I will have to at some point. Or maybe I have to go back to Linux Mint