Renault Kangoo flashing stop & battery indication lights when driving

This problem started today. When I am driving the Stop and Battery lights on the dash flash. Will the motor running in idle I have placed a multimeter across the battery terminals and there seems to be a surging happening where the reads approx 12.15V and then surges for a couple of seconds to 12.9V as if the charging circuit is cutting in and out. Has anyone had this problem before and if so can they help me please.