Hi,
The Self Assessment tax return is used by non UK tax residents, to declare all of their UK income, which you advise is income from property and bank interest on SA100 and SA109.
SA109 confirms that you are not tax resident and allows you to claim personal allowances. As a non tax resident, some of your income is disregarded when calculating your tax liability. Have a look at helpsheet HS300 or more information:
HS300 Non-residents and investment income (2024)
If you are required to pay UK tax on your income, you can claim a tax credit in Australia for the tax paid in the UK, under the double taxation treaty.
Thank you.