Hi Ray and Barbara,
Welcome to the forum.
Sorry I don't know much about this one. It's something I may be investigating soon once my parents have decided whether they want to move out here or not.
Have you tried talking to any emigration agents since they may have this kind of info?
As far as I'm aware there isn't a refundable 10 year deposit it's just that the Assurer needs to pay for certain welfare costs as I understand it. The Assurer must meet some requirements though and be earning a certain salary (I don't know what that is though).
Australian Immigration Fact Sheet 34. Assurance of Support
The Centrelink payments doesn't mention Medicare
Assurance of Support
I know that the pension is frozen when you leave the UK and I've just had a hunt around for other info (since I may be needing this myself

)
Foreign pensions and annuities
seems to say that yes you pay tax on your pension.
However you don't have to pay double taxation if you've already paid tax on it in the UK according to
Foreign pensions and annuities
I found one website that says that anyone paying tax on a UK state pension are entitled to a rebate based on the contributions made but it wasn't on on official website so I'm not sure if that's accurate.
Have you tried calling the
Australian Taxation Office Homepage and asking them? They seem to be more helpful that the UK one.
Regards,
Karen