well first you take your existing key to the vw garage and they will charge you around 50-100 pounds. if u dont have the original key then u need to contact the garage where it was first sold and get the immobiliser code :)
I had a key made recently and ther are 3 charges involved. Because I did not have the key number this would cost me about �25. The actual cost of the key with chip installed is about �30. You then have to take the car to the dealer to have the key programmed which costs about �40. One big rip off!