I'm afrfraid the problem remains unresolved. I contacted Chrysler (which is now Fiat) iand apparently there is only one place that 'may' have the original Chrysler software capable of diagnosing this issue. This was a small independent near London, however they could not guarantee that it would be successful and it would require taking the car from Manchester to London via a recovery service (as the testing station was unable to issue an MOT certificate).

I think I may end up changing a few of the ABS parts as a process of elimination. It's not ideal and I'll be using used parts due to cost, however I'm really out of ideas now.