You Do Need power plug adapter while traveling from Great Britain to South Africa.

Here is Why You Need An Adapter

The outlet and plug type used in South Africa are C, M and N and in Great Britain is G. This is how they look like.

Great Britain

In Great Britain, outlets of type G are in use.

Type G

South Africa

In South Africa, outlets of type C, M and N are in use.

Type C

Type M

Type N