How can I fix my Peugeot Satelis 125?

Hi I have a 2006 Peugeot Satelis 125 a few weeks ago I noticed that the oil pressure light was coming on intermittently. And I topped up the oil. All was good for a few days until I noticed that at low revs ie going around a tight bend or starting from a traffic light the bike was struggling and hesitant just for a second to accelerate. Over the next few days the problem got worse with more frequent episodes of power loss and for longer periods, which would seem to correct themselves temporarily after re starting the engine. At last the bike gave up accelerating at all but still starts fine. Its in the shop now but the mechanic is still puzzled. He seems to think its an electrical issue . Could you suggest any other explanations. Thanks.