Got this back from Apple support;
Greetings from iTunes Store Customer Support. My name is Ajith and I am happy to assist you today.
I understand that you you have change the country associated with your account to Australia and now unable to see the purchased apps from the United kingdom iTunes Store.
Darren, I would like to inform you that after you change countries, you will no longer receive application update notifications in iTunes for the apps you purchased in your original country. However, you'll still receive update notifications on your iOS device for any applications installed on it.
I hope this information was helpful. Thank you for your patience and understanding in this matter.
If you have any additional questions regarding iTunes Store, please write to me and I will be happy to assist you further. I am sure that you'll continue to enjoy the iTunes Store.
Have a nice day!