Going straight into medicine I think is the best option although it is incredibly competitive. Why do you want to get a biomedical science degree first? It would provide a solid base for your medical degree.
I know some unis say that you can transfer mid-first year into a medicine course assuming you have the correct requirements and there is space on the course.
And you can definitely apply to get a postgraduate student I think you get an accelerated course of 4 years instead of 5.