Ho hum, The Ecu firm would not let me bring the ECU in because they "needed to see the car", so I booked it in to be done.
I dropped it off this morning, and walked to Braintree railway station and got a train to Manningtree. I was sat on the platform at Manningtree, basking in the sun when I got a phone call from said ECU firm to say they could not do the job because the ECU is too difficult to get out.
So I made my way back, and they are now happy to do the job if I can arrange someone to remove the ECU from the vehicle. Unlike many ECUs my one can't be accessed via the diagnostic port.
Looks like another DIY job to get on with.
One good point is that I will save £125 by doing the remove/refit myself.