As a UK national and resident, you are liable to tax in the UK, arising on all your worldwide income and gains.
Article 17 of the UK / Australia double taxation agreements advises, that Australian pensions, including Australian government pensions paid to the resident of the UK, are taxable only in the UK. You can see information here:
UK/ Australia Double Taxation Convention
Your Australian pension, should be declared in a Self Assessment tax return.
You should also contact the Australian tax authorities, to find out how to claim a repayment of any tax paid in Austrlia, as the pensions are not taxable in that country. A foreign tax credit can be claimed in your Self Assessment tax return for foreign tax paid.