Silly, silly, silly - I have to say that I'm starting to tire of all this pedanticism over words (not to mention that the attempts at semantic sarcasm may totally confuse many forum members) - have you nothing more useful to write?I don't think having two RCDs would help. I suppose if one develops a fault, you could fall back onto the other but is that level of redundancy really necessary? ... Additionally, I don't see why the user would want to install a socket in his consumer unit. If not for the reason that it would take up far too many slots, then while I understand that one can get a DIN mounted socket, I think you'd struggle to attach it to the bus bar.You should install a double RCD socket, if none exists in the existing consumer unit.
Kind Regards, John