UK without a Visa

Hi all,

I'm currently looking at doing my first world packers exchange in June when I come back from a brief stint in Europe. I am Australian which means I can stay in the UK for 6 months without a visa as long as I don't work. I was thinking of just doing a world packers placement and not saying I was volunteering because I guess it's technically not work? However, some places I have looked at want you to have the visa. Has anyone worked without one?