The immobiliser light is not flashing when the key goes into the ignition. It stays a constant red along with the stop sign that stays on red (and some other lights at the bottom which normally go out when the car is started).
Also I don't think it is anything to do with the key as I have used two different keys both not working.
-- It is worth mentioning that before this problem of the car not starting at all, the car was 'concking out' after it had been running and moving at speed, then slowing right down and not moving at all, for example coming to a stand still on the motorway or at traffic lights. I had decided that these were two seperate problems but perhaps not?