Transit through Beijing to melbourne

Will you fly from UK? You really needn't worry about this because you are qualified for 72 hours free transit there. However, the premise is that you don't stop by any other Chinese cities. If you meet the requirements, then you just need to apply for the free transit when you arrive.

If you fly with connecting air ticket, then your luggage should be sent to your finnal destination. If you fly with two separate different airlines, then usually you should claim your luggage and check it again. However, I still suggest you confirm this with your airlines. Sometimes, even two different airlines might have an agreement to carry passengers' luggage to their final destination.