I’ll preface this post with saying that I am totally unfamiliar with the Sport, but can give you some info regarding the 1.6 engine, someof which may be comparable.
At least for the 1.6, the fuel pump relay and main relay are the same type of relay. You advise that your F1 (yeah, FI, etc) fuse blows with the key in the on position - when the main relay is energized. Put the fuel pump relay in its place and turn the key on - obviously, your fuel pump will not work, but this will determine if there’s a short in the main relay circuit.
In the 1.6, the F1 fuse circuit is pretty intricate:
From that main relay, that blue/black wire runs to the fuel pump, the EGR solenoid, the EVAP solenoid, torque converter (if auto), idle speed solenoid, distributor, injectors, o2 sensor, etc.
If you remove the fuse, and use a test light in its place, you'll see that the light will be bright, as there's a short in the circuit somewhere. If you then disconnect each one of the components that the blue/black wire feeds to, when your light goes out, you have found your short. Saves going through a box of fuses.
The fact that you say this is happening intermittently - every few days, etc., - would seem to indicate that there is a wiring short somewhere, rather than one of sensors.