Bannock,
Presuming that you are referring to a UK mil pension, and it is taxed upon payment......Both tax depts have an understanding not to double tax. Both Inland Revenue (IR) and Aus Tax Office (ATO) share tax info on those individuals who pay tax in the two countries - however, your TOTAL income will be utilised in Oz to determine what tax bracket to draw tax on the Australian component of your wage - ie probably the 'Top' rate - 49%?? - or something close to it if your Pension is anything worth 'retiring' on AND you get a half reasonable wage in Oz. If your wage in Oz is in a lower tax bracket - probably the case, you will get notification to pay the extra tax after Jul 1 (due by the following March each year). Annual Tax returns for all income earners are compulsary in OZ. An accountant will cost you $200 per year to assist in BASICS (recommended). Initial consultations etc will cost more in year one - just to spend the time to fully explain and document your situation.
If you pay no UK income tax on your UK pension, you will pay FULL tax on it in Australia.
I am not a financial advisor, I just have a little info on shared tax agreements. - treat ALL advice cautiously....
http://law.ato.gov.au/atolaw