Thanks for your question
How did this money arise - was it earnings whilst in Australia, or investment/savings income you took out with you, and are now bringing back into the UK.
Sale of property?
All of the above,an accumulation of property sale,savings nd investments over the years,
Perhaps you can expand
1) did any of these investments arise from the UK, have these been declared to HMRC over the years
2) When was the property/properties sold, which country is the property in, was it your main residence
3) Were the savings accumulated whilst in Australia, or did you have them when you left the UK
4) When did you return to the UK, and how much of a gap was there between your return to the UK and you arranging transfer of the money.
I need to know the history of each of the monies, and how and from where they arose, so I can advise whether any tax has to be considered in the UK