Golden syrup

Have you looked in GB rue des Tongres? They have a baking section with some British brands.

Some Delhaize shops also sell Golden Syrup, but I can't advise a specific one in that area. And the bigger Carrefores - not much use to you, but I think I've seen it in the big Carrefour out at Kraainem.

The larger Delhaize shops do indeed have Tate and Lyle's. the one near Flagey for sure.

GB in thiefry has it! check american/english section by the drinks