To round this thread off...
The new Starter Relay arrived on Saturday and (after a lot of cursing and swearing at the connector on the top which would not come loose!) I managed to swap it over and, Glory Be! the bike started on the button
So if you get an Error Code 12 on the instruments, but the resistance on the Crank Position Sensor is good and the continuity between the CPS and the ECU is fine (IIRC it was pins 6 and 9 on the top row of the ECU connector, counting from the left side of the bike) and your clutch switch, neutral switch and side stand switches are all ok, try bump starting the bike or shorting across the B and M terminals at the bottom of the starter relay.
If it fires up ok like that, then it may well be the Start Relay is knackered.
It's dead easy to fix (if you can get the connector to the loom to come off!), just disconnect the negative battery terminal, then lift the relay off its mount, unscrew the connector to the starter motor and the positive battery terminal, put the new relay in and connect back up (always do the Negative terminal LAST!) and you should be good to go