Hi Annalouise -
I've just sat and passed the National Psychology Exam. Unfortunately you will need to complete a transitional programme including sitting the exam regardless of your years of experience (I qualified as a Clin Psych in UK in 2005) - 3 months is the minimum you would have to do. The issue I see is if you are less than two years qualified as this seems to be a minimum time of supervised practice required AFTER qualification needed in order to call yourself a clinical psychologist here. You'd be best to check the AHPRA website/contact them directly, but I would imagine your transitional programme would be longer without a few years experience post qualification or they might make you do something additional regarding supervised practice. AHPRA is a headache, time consuming, very frustrating and expensive - lots of hoops to jump, but I think the transitional programme is the most difficult to secure - everything else seems to be paperwork and waiting so far for me.
To to answer your other question, you can get the APS to assess your academic qualifications from the UK, which is a good idea as it can take sometime. However, you can't apply for provisional registration until you have a transitional programme in place (which would be fairly difficult without being in the country).
Hope this is helpful.