As a follow up to this I have been having a look inand to this a bit more I think the symptom is pretty much as described in many other posts on here caused by damp but it's getting worse. As Richard said above the odometer reading failure is most likely internal as the reading is stored internally, it may help to clean the ribbon cable connector and if a hair dryer doesn't work (it's MOT time) I may try that and to that end I found the post below from IVO with a youtube link to a video explaining how to do this
