promotion code for britishairways.com

My brother needs to book flight tickets to canada between 20th August to 10th September. He travels through british airways only since it seems to be the only airline offering premium economy seats. He insists on booking seats through ba.com or britishairways.com only because it gives the flexibility of choosing seats as per your liking.
I am looking for promotion codes which may be applicable on this site..avios points are not applicable on the flight he is trying to book