The double taxation agreement between the UK and Australia, at article 10, advises that dividends from Australia resident companies, owned by a resident of the UK, may be taxed in the UK.
However, it also states the dividends may also be taxed in Australia, but that this is limited to 15% of the gross dividend. Please see -
UK/ AUSTRALIA DOUBLE TAXATION CONVENTION
As you are resident and domiciled in the UK, HMRC has the right to tax your world-wide income. This includes the Australian dividends, which you should declare in the foreign section of SA106.
You can claim a foreign tax credit for the foreign tax paid, up to a maxmimum of 15% of the gross dividend using the form here -