Unplug anything in that socket circuit (if anything), buzz or insulation test between L-E/L-N
If it is not clear (probably won't be), disconnect one leg of the circuit at C/U and break the ring at a mid-way point in the socket ring, so the ends are disconnected and in theory makes two radial circuits.
Energize one leg (obviously the open ends at the socket would be terminated separately so they aren't just hanging), if it pops off then you know it's on that energized leg, then try the other leg and see which sockets are on with plug in tester . Start unscrewing ones that are not energized and visual inspection for incorrect termination/squashed cables/nicked cables etc etc
That is how i did a fault the other week with socket rcbo keep tripping, find offending socket and turned out to be L-E as live was poorly terminated (a lot of copper showing outside of terminal) and touching the metal back box causing it to trip off.