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

Here is Why You Need An Adapter

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

South Africa

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

Type C

Type M

Type N

Great Britain

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

Type G