Sean, tax wise it always depends on your visa type/residency and other factors to see how you are taxed. Either way you will only pay tax on the difference between the Income from the rent and your expenses on the UK property. If you pay tax in the UK then when you declare the income here you get tax credits here so that you do not double up on tax. This is just a rough answer so if possible contact a registered tax agent or accountant like Alan Collett on this site or his website
Go Matilda - Your Gateway to Australia - Visa, Tax and Financial Planning for Australia for personal advice on your own situation.
Good news is that your primary residence is Captial Gains Tax free under Australian Tax rules and remains so for 6 years after you leave it, even if you rent it out! But beware if you buy in OZ then you can't claim CGT relief on both the UK and Australia for the same period. I always recommend people rent for the first year here and make sure they like the area before buying. We moved twice before we finally bought and are so glad we did not buy on first impressions as the area we settled in first looked great but had no services for working famillies.
Liam