OK, so I took My little terror to a local Alfa Specialist, difficult when one can only drive in 1st and 2nd.
He says I'd managed to scramble the computer!
Apparently when re-connecting the battery one needs to ensure an immediate fit, not allow for any sparking.
He's reset the computer, and done some proxy alignment setting the baud rate to 9600, reckons there are 4 computers that need to be in sync.
Also done a software upgrade!
Will pick it up this evening, give it a test then!
PS, any ideas whether I need to connect both power cables (from old radio) to the new radio.