I keep the plastic key in my wallet, and it does contain the matched transponder, and will start the car. I bought my car as a CPO from a dealer, and as it only had one key they had to order both the second remote head key and the plastic key from BMW. I had to insist on the plastic key, as they were originally only going to get the second main key for me.ZedFourM said:
An "emergency" key (like the plastic key provided with the Z4 in the UK) is designed to open the doors/boot/glovebox in an emergency (e.g. when you have lost/forgotten your main key or locked it in the car). It does not contain a transponder and will not start the car. Replacement cost is about £38, and expect to have to show a copy of your V5 to the dealers before they will sell one to you.
If you've got a plastic key, go try and start the car with it - you might be pleasantly surprised ...
Key assembly was now to thick to fit into case!! Sent the bits to Ben and he rescued the situation with a repair and new case. LESSON LEARNED!! Key works perfectly. THANKS