In case anyone suffers a similar water leakage I have managed to find the culprit. This particular car was in an accident and was 'professionally' repaired. On the well below the windscreen below the windscreen wipers (covered by plastic cladding) on the passenger side is the induction fan for the cabin ventilation. The cover from this was missing as is the filter (if they come with a filter), the plastic cladding had been put back on haphazardly and did not seal the water from dripping down into the fan, which got into the vent duct and dripped down the back of the carpet into the passenger footwell right where the ECU is mounted.Happily repaired the leak now (amazing the uses of a bicycle inner tube combined with grease) and still drying out the car, but no more leak. Hurrah!!!