It has one already. Petrol engines have to have throttles. Diesels, by nature of the way they work, don't. But that's a different discussion.
With a 1.2 8 valve engine there will be no benefit at all from fitting separate throttle bodies. There is never any point in a car with single point injection. (I do not know whether or not your car has multipoint injection). A 1.2 litre car engine is not drawing anywhere enough air to take advantage of separate throttle bodies. Bikes are different, the engines commonly spin at 18,000 to 20,000rpm.
Fitting a separate throttle body for each intake tract is a technique used in high performance engines to allow for sharper response to accelerator inputs and also to reduce intake vacuum and better airflow during high rev and high load operation.
Something that's required for good air/fuel mixing is a decent airflow velocity, or speed. If you were to fit separate throttle bodies to your car you will probably (almost certainly) find that the air/fuel mixing is not as good as it is with the standard setup.
This will lead to inferior torque delivery, inferior performance and inferior driveability in general, along with poor fuel economy.