If you have paid tax on the income in Australia and the income is also taxable in the UK, then you may be able to claim up to 100% credit for the tax paid in Australia. This will depend on the type of income.
Your UK liability is calculated including your overseas income. If the UK tax payable on the overseas income is equal to or greater than the tax paid overseas, then the credit may be 100% of the tax paid.
If the UK tax on the overseas income is less than the Overseas tax, you can only claim a credit to cover the UK tax on this income.
Dividends are treated differently, as only up to treaty rate of the overseas tax paid, can be claimed as a credit:
Double Taxation Relief Manual