What is the calling code for ringing an autralian mobile from England?

Australian mobile numbers start with 04, which becomes +61 4 in international format.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, and many other countries use different prefixes.)