My Fiat Grande Punto Active 1.2 has been doing this since May but has recently got worse. Sometimes when starting my car, it grinds when turning the key, really loudly. I am unsure whether its the starter motor or whether it is the flywheel.

As in a screeching noise?

Hi Sophie and welcome to the forum

If it's only during startup it's likely to be the starter, as flywheel issues would probably be apparent all the time. What would be helpful would having someone trying to identify where the sound is coming from, while someone else tries to start it, and if they could video it and post the video here someone may know the sound and be able to tell exactly what it is