Assuming a UK supplied car, the Mk2 has an immobiliser and came with two keys and each has a chip. Therefore you cannot start the car without a chipped key.
Are you talking about an aftermarket sendor dongle.
Timpsons can read the number off a key and cut a new one and write the electonic number to the integrated chip.
99 Mk2 1.8IS
08 Mk3 2.0 Sport RC, Drumtochty Glen, Auchenblae,