Received by email.
You must already be registered on Amazon.co.uk or be willing to move/register a new account there.
See - International Availability & Transferring Your Account
Note: Amazon may ask you for proof that you reside in the UK… See - https://www.ozbargain.com.au/node/156642
Personally I don't think it's very likely but it is a possibility.
Disclaimer:
Not actually sure if any of them are good (or good value)… Let me know what's good in the comments and I'll add to the description.
You will need your kindle attached to a ".co.uk" amazon account.
I believe they will not be available if you have amazon.com (or .au) as your norm.