If you want to use Uber when you get to the UK, you'll need to update your Uber profile with your UK mobile number. Uber drivers won't want to call/text your Australian mobile number.
Updating your Uber profile with your UK mobile number is easy. Just do the following:
1. Open the Uber app on your phone.
2. Tap the little profile icon in the top left of the app, then tap Settings from the menu, then tap "Edit Account". You'll need to sign in with your password.
3. Once logged in, you can change your mobile number to your UK mobile number. Remember that your UK mobile number, when written in international format, is +44 then the UK mobile number with the leading 0 removed.