Possible reasons for check engine light - 2004 fiesta?

Hey everyone,

Planning on getting the AA to come take a look with the breakdown cover I've got, but just hoping to get an idea of what might be causing this light to come on before hand so I'm more prepared.

So I've had the car since 2018, done 50-60k miles (it's got 128k miles total). I drove it up town on Saturday, no issues. No light, car felt fine to drive, no issues at all. Stayed up town for a few hours, then on the drive back in the evening the light came on and has stayed on since. I haven't put any petrol in the car for a little bit now as I've started not to use the car as much - may have even been over a month ago but it's got 1/2 a tank still. It only had its MOT last month.

On the drive back I haven't noticed any issues either, it all still feels perfectly fine. I don't think it could be as simple as the fuel cap as I haven't recently put petrol in? So likely something more seriously but not "car damning" yet?

Any ideas?