What do BBC studios use for speaker cables

While I can't give you a direct answer, I can suggest that you go to the Harbeth website, where there are faqs and a forum for Harbeth users. I looked at it a while back (when I got my Harbeth M30s) and my recollection is that, frankly, Harbeth is not too picky about electronics or cables (at least in theory). I recall Alan Shaw, the owner, remarking to the effect that he wants the Harbeths to work well with relatively modest equipment. I use Cardas Cross, myself, which I think is just a basic, but very high quality copper cable that leans to the warm side.

Despite what Shaw says, I've found the Harbeths to be fairly sensitive to the equipment that feeds them. It's been my intention to buy a set of the better Linn speaker cables and try those, just for fun. I think they should be just fine.

BBC are not known for paying big bucks for speakers or equipment. Many of the successful BBC designs like the Rogers were in fact very economical (low cost) speakers that sounded very good.

I doubt BBC would use special cables, as large companies are sensitive to cost on items that are widely used. Ordinary stranded copper wire would be my guess.

Here is a link to a site that can help you

I have a pair of Rogers Studio 1 (Justlike your BC1). I've tried alot of things and found the AP oval 9, Xindak FS0.5 to work the best. I'd like to try Cardas Golden Reference though.