Thanks again, Paul. I changed the bank 1 lambda sensor, no probs with new error codes or running issues. Unfortunately though, it hasn't stopped the EML coming on, so ill have to move on down the list of possible causes. I haven't been able to obtain the error code yet.
The issue, i would say is clearly linked to ambient temperature because on a warm day, as soon as you put the engine under a bit more than normal load (maintaining speed going up an incline), the light is triggered. doesn't seem to happen on cooler days. Still doesn't seem to affect running/power & always resets on shutdown/start-up.