Any ideas re: Sole trading as a pilot

[Stuck in a moment...]

I am currently fully employed outside the aviation industry, but have managed to gain part time position as an FO with a small charter as well. They can only pay flight time at the moment and therefore no salary. Has anyone tried to become a sole trader (ie self employed) to cover the tax issues regarding the extra income?
If so, some guidance would be appreciated.
Thanks.:confused: :confused: :ok: