Hi
wait for sponsorship having been approved and then ask police certificate to be mailed to your visa office.
No you don't , the OP's application is being processed in London, he applies for the police certificate and has the Australians send it to London. London can match it up with the Name and DOB to the file when it is created. If you wait until London sends you the file no. (They don't normally send AORs in Sponsorship cases) you will add another 3/4 months to the process.
PMM