Preheat oven to 180 C / Gas 4. Lightly grease a roasting tin.
Mix venison, sausagemeat, onions and cracker crumbs in a large bowl until well combined. Add the evaporated milk, eggs, barbecue sauce, salt, pepper and half of the passata; mix until evenly combined and let stand 15 minutes. Place onto roasting tin and shape into a loaf.
Bake in preheated oven for 30 minutes. Spread top with remaining passata and continue baking for an additional hour, until the internal temperature reaches 82 degrees C.