How do I cure Peugeot Elystar cutting out while running?

My '03 Peugeot Elystar starts ok, will run fine and drives ok but dies whilst running at random. Sometimes will run for minutes, somtimes will only run for seconds, Sometimes dies on tick over. Length of run time totally random.
Had it serviced by local peugeot dealer who said they had "used the box on it to clear out the fault codes". They have had it twice to try and cure it but no joy.