If he makes a habit of running it to empty, it might also be that sediment has found its way into the engine - unlikely but it does happen.
As for 97RON in a 1.2, i don't see the problem with feeding the car a better quality of fuel every now and again. To be honest, i really don't notice any difference between 95 & 97RON in my 172, but thats a whole can of worms right there.
@ben_p, yes they offer 95RON as do all petrol stations, however their Super unleaded is indeed 99RON. But it doesn't have additives like BP Ultimate (97RON) so it doesn't clean your engine as thoroughly.