From the unpredicatability/irregularity of the ABS/SERV lights, it sounds like there's a loose wire/connection at one one of the wheel sensors.
thing to do is to remove each wheel one at a time, and visually inspect the wires at the sensors.
Start with the front wheels, as the sensors are easier to locate (they're just behind the brake disc, infront of the caliper (I think))
...while you're there, also check that there's no debris between the sensor and reluctor ring (the notches on the CV joint). There's one sensor per wheel.
But before you take the wheels off - visually inspect the wires running into the
(centrally located at the back of the engine bay - looks like a small, steel, tamperproof box).
Don't open the box, but look at the wires running into it - check that the box isn't chafing any of the wires. ...apparently, on some Clios, the vibrations of the engine can cause the steel box to cut into these wires - resulting in short-circuits which confuse the
I empathise with your "niggle", but don't think there's much to worry about - unless the
look worn/damaged - in which case I'd get that particular wiring loom replaced ASAP.
I would note that from my recent experience with my Clio - while the ABS/SERV lights are on, the ABS system is off, and vice versa