Tried disconnecting the battery for days, still had headlights on and flashing indicators when the battery was reconnected, and still immobolised.

Eventually, today I had another go at it, me thinking that the alarm module batteries are dead, and the immobiliser might be thinking the alarm has been disabled.
Disconnected the headlight connectors, connected the battery and hooked up a battery charger, and left it till the charger said the battery was fully charged.
Attempted a start with the battery charger still connected, (me thinking the charger would elevate the system voltage to allow the immobiliser to see the alarm module), and the immobiliser magically reset and the car started.
Reconnected the headlight connectors, and new problem, the high beam headlights come on when the engine is turned off, and the doors will not lock/unlock via the key fob, but will via the centre console button. So I have disconnected the battery again and will leave it a day,hoping it resets itself and then will try it again.