I gave in and bought a complete secondhand steering column (matching ECU number). I swapped out the ignition barrel and the black plastic ring near the key. Turn key to just before ignition and all lights go out (except airbag which i know about) - Car will not start. Engine is turning over fast enough to start and it used to start first turn. Is there an imobiliser somewhere that needs to swapped? The key code light stays off. (Car has been standing for several weeks)

To clarify what you are saying:

When we all turn the key to 'ignition on' the car does a self test and the display eventually only shows illuminated symbols for the problems.

So with ignition on and the engine not running you should have at least the oil warning light for no oil pressure and the battery light for no charging.

So it is not clear what you mean by "Turn key to just before ignition and all lights go out (except airbag which i know about)"

When you first turn to 'ignition on' you should see the key code light which then goes out if there is the car is not immobilised

You can check the immobliser is working by wrapping the key in many layers of aluminium foil getting it as close to the metal part of the key that goes in the barrel as you can. The light will not go out with the key in with a few layers of foil. Even if the car is immobilised the engine will still turn when you fully turn the key.

If the code/ immobiliser light comes on then goes off,it should not be a code fault.

If code light / padlock goes off when you first put ignition on = not an immboliser fault

Id be checking for spark and injection
If no spark or injection id be checking crank sensor / air gap / phlonic wheel been fitted in the correct orientation

Ziggy