If you are just travelling and not moving to the UK, do not attempt to change your iTunes Store account to the UK store. You would need a valid UK payment method and billing/mailling address to make the change, and would then have to repeat the process to switch back to the Australian iTunes Store when you get back to Australia. You would then be cut off from updates to any apps you purchased in the UK store.
If you do have a valid UK payment method and billing address, it would be much more practical to just set up a new account in the UK iTunes Store and leave your Australian account as it is.
Regards.