2001 mk2 punto fires on cylinders 2&3 only?

2001 (51 plate) Punto mk2 has started firing on 2 cylinders only. 2&3 work great, 1&4 nothing. I have checked out the distributor packs and these seem OK when I swap them over. I've checked out HT leads and no sign of a spark in cylinders 1&4. I've checked out wiring - as much as I can and cannot see anything obvious, damaged etc. Could it be the ECU module? or is there something else I need to check.