#3 - Oct. 5, 2010, 8:34 p.m.
The only version of World of Warcraft sold in the UK is the European version, Rorayia.
Since you have a North American account, you will have the option to download the game from the website when it becomes available. You may receive an error in processing the credit card since you are upgrading from an unsupported region. If you have an issue with the upgrade, you may wish to contact Account Services by phone for assistance.
Alternatively, if you still have friends or family in Australia, they could purchase the game from a retailer and then email you the authentication key. You can then use that key to upgrade the account and not have to worry about the online upgrade process.