What are the obstacles / possibilities in getting a work permit to stay in the UK for about 6 months, as a self-employed person?

Most of my income, as a Pastel consultant, is derived from remote desktop support, so I can technically work from anywhere in the world, provided I have internet access.

However, the immigration regulations in the UK might not allow me to do that, as a South African passport holder without a job offer from a UK employer.

Any ideas as to how I can make this possible?