Right. I've gone back to the beginning of this thread. If they are now saying the ECU is at fault then i think you should let them fit a NEW one supplied by Nissan (you want to see the paperwork). Id also ask for the faulty one back so you can send it to Nissan for diagnosis. When you are convinced that you have a new ECU, if the EML continues to come on then you will take the car back and demand it be diagnosed by a Nissan sports car dealership. And you also need to write a letter saying that as the fault occurred within the warranty period you dont accept any expiration of the warranty until fault resolved.
If the dealership is still being aggressively defensive about this, write to their head office. And keep all correspondance youve had and insist any further work or examinations of the car are documented in writing.
Its relatively easy for us to offer advice but I'm afraid you are going to have to do all the leg work.
I think you are in the Plymouth area and if it would help I'm prepared to come along with you to EH and sit in on a meeting as former Chairman of the NMGB recognised nissan sports cars owners club.
I am not sure which ECU the zed will need, so I can't look for a price.
You are correct regarding our location, We would appreciate your kind offer very much if it comes to that.