In a medium bowl combine the mince, egg, tomato sauce, barbecue sauce, Worcestershire sauce and onion. If you are using the vegemite throw it in too. Mix together using your hands until well mixed. Add only as much flour as necessary to keep it from being too runny.
Heat a large frypan over medium heat. Form the burger mixture into 4 large patties. Place patties in the hot frypan and fry until no longer pink; about 7 minutes per side depending on thickness. Serve on buns or with gravy.