The phrase "affiliated supporters" refers to people who are connected or associated with a particular group or organization and show their support for it. Full definition
In addition registered supporters — not drawn from unions — will be able to sign up with same rights as affiliated supporters. (theguardian.com)
The unions might run campaigns to convert members into affiliated supporters but it is not clear how many would be interested. (theconversation.com)
Individual voting in closed primary by party members, registered supporters and affiliated supporters on same basis as national leadership election. (theguardian.com)