I reckon it'll be the same at the UK, i.e. it's cancelled as soon as the application is received. However, only the Aus immigration will know that so it'll be fine for travel anywhere else, although not much help in your case.
https://www.passports.gov.au/passport-care/passport-validity-and-foreign-visas#:~:text=Can I use my current,Australia using the expiring passport.