Only a suggestion. Find the fuse it's on and if it's seperate from the ignition one take the fuse out then see if it starts.
I had to do this once with central locking as I unlocked the door it re-locked itself before I could get the door open I was advised to remove the fuse and lock doors manualy.
Alternatively is take it to an AUTO ELECTRICIAN not a mechanic they have testing equipment that may find the fault.
bob
October 2005