Andy, for the cost of a set of correct plugs and the loan of a proper Peugeot coil pack from your friendly car sales or neighbouring garage, worth the effort.
You may well be right that the ECU is going down, probably because it has been spiked by a faulty or cheap coil pack.
Peugeot dealer would sort this car. He would fit a new ECU AND a proper coil pack. Some of the early genuine Peugeot coil packs gave trouble like this, Peugeot then uprated them and in later years only fitted one type (Bougicord, I think). I am also sure that later models have the suppresser fitted internally.
Course, I am probably completely wrong! Gwyn