Perhaps Simon from Harman Technology will step in and clarify. I, too, find it difficult to imagine Swan running two separate B&W lines, one with Ilford chemistry and the other with Clayton. It seems much more economically feasible to just switch B&W processing in their lab to Ilford, as that's what being an "Ilford" lab requires. So, that would then lead us back to one of the original questions: What would justify the added expense of Ilford-branded processing if it's done in the same lab, using the same chemicals and printed on the same machines using the same paper as film sent to them under the Swan or The Darkroom banners? I love Ilford, but I'm not so sure that something like, "The difference is Ilford quality control" would be enough to sway me to pay the extra bucks, as Swan seems to have awesome quality control already.
The small lab I use offers 7 different B & W developers and their turn around time is very fast so I dont see why other labs cant do this.