Ok, so back to the old door switch / interior light issue. Read a few threads which all point to the Microswitch being at fault and a good dose of WD40 should sort it.
So, I did that based on the fact that the dash was displaying the door open symbol when in fact it was shut and the interior light was on permanently.
The issue has changed in that the door open symbol (dash) is no longer showing and the interior light pulses evey second or so with a click from the dash... which is also setting off the alarm!
So, with the new problem in mind I've followed advice and links in the threads which pointed to cracked solder on circuitry - admitedly this was for a MK4 VW but I was taken there via a link from this site.
Anyway, upon investigation the door mech in my 2001 A3 is nothing like that of a MK4 and so the cracked solder issue seems like a red-herring. However inside the door there is a black module with 3 inputs located just below the window-line about 1.5" x 1.5" and sealed, plus the mechancical door gubbins with the micrtoswitch.
So, any pointers to to which I should be replacing given that the visual symptoms have changed from being a static linterior light and open-door symbol on the dash to a pulsing interior light, no symbol on dash and the alarm going off (cos it thinks the door is open).
Module or Mircoswitch? Admitedly, I don't know if this wee black module has any bearing on the issue but its the ONLY other thing inside the door that appears to be electronic and poss related to the the door / window operation.