GlobalCountryCode.org is your comprehensive resource to help you make calls anywhere across the globe. This page details how to dial Australia from United Kingdom.
To call Australia from United Kingdom, dial 00 + 61 + the number you wish to connect to.
Most mobile phones and smart phones have the "+" sign on the same key as "0". To call internationally from most mobile or smart phones simply dial the "+" sign, followed by the country code, city code and local phone number as shown above.
TIP: If you travel abroad often, save all the numbers in your contacts with the "+" sign. The sign will be ignored when you're at home but will save you the hassle of redialing numbers when you're abroad.