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As you yourself checked and stated, you do not need a visa to visit either UK or Norway as a tourist (with an Australian passport). As long as your stay does not exceed maximum allowed (usually 90 days), you can travel freely between the two countries.
I have heard anecdotal evidence that if you leave UK and come back "quickly", an immigration officer in the UK may decided that your short trip doesn't count as to end the first stay and start a new one. In fact, I personally know one person that ran into this scenario (with a USA passport) - but he went to France for 1 day - and thus effectively came back to the UK on the same day as he left. As he was still within the 90 days for the UK, it still wasn't an issue though.