This question already has an answer here:
If I am an Australian entering the UK without a visa and I travel back and forth between EU and UK during the 6 months, will I be free to get another 6-month stay beyond the last day of the 6 month period? I have heard something like the limit for an Aussie without a visa in the UK is 6 months stay within any 12 months time-frame but I'm not sure if this is true? Ideally, I'm looking to be abroad for 12 months without a visa hopping between UK and EU/Africa - no work required. I just don't want to end up in immigration trouble.