Patience had finally paid off. Sitting in the garden with a cold cider on the hottest day of the year I think that after over 30 years I have identified this coin.
I knew it was Mamluk but I just couldn't get it. In one final attempt with Balog, Coins of the Mamluk Sultans, I have it. Al Nasir Muhammad, 709-41AH (1310-41AD) copper fulus, third reign , Cairo mint, Balog 221.