Once you have lodged a valid sc.820 visa application, a BVA will be granted automatically. The BVA will come into effect when your current visa ceases. You can apply for a BVB wether your BVA is in effect or not. If you leave and return while your tourist visa is still valid, it will trigger a new stay period on your return and the Bridging Visa will remain dormant until the tourist visa ceases.