Freddie -
One question that hasn't been raised in this thread is what sort of visa are you proposing to get to enable you to come to Australia?
If you intend to get a Retirement visa, then that will be the 405 Investor Retirement visa, which only gives you Temporary Residence (albeit for as long as you want to live here - permanently if you want).
If you are coming on a Parent visa, then it would give you Permanent Residence.
The very significant difference is that Temporary Residence gives you a very great tax advantage in that only your Australian income would be taxed in Australia, and your other income (including any income which you took in the UK from your pension) is taxable in the country of source (UK in this case).
This means that you can get the tax-free allowances and the benefits of the lower bands of taxation in both countries - and believe me, that can amount to a very substantial saving in the overall amount of tax that you would pay, particularly if you are in or close to the 40% tax band in the UK.
Some people will tell you that there are moves to obtain Permanent Residence for holders of Retirement Visas - and that of course would remove the tax benefit I have described - but my personal belief is that it will never happen in the foreseeable future (almost certainly never for 405 visa holders, even if it does eventually happen for the old 410 Retirement visa - and I personally doubt even that).
Regards,
Howard