The vote will include: British, Irish and Commonwealth citizens over 18 who are resident in the UK, along with UK nationals who have lived overseas for less than 15 years. Members of the House of Lords and Commonwealth citizens in Gibraltar will also be eligible, unlike in a general election. Citizens from EU countries - apart from Ireland, Malta and Cyprus - will not get a vote.
In other words:
If your a British citizen and you've lived in Australia for the last 13 years - you can vote.
If your not a British citizen and you've lived in the UK for the last 13 years - you can't vote.
What's so special about Cyprus and Malta?