Sandy,
It was put on to the lower whipping of the butt ring as well. My Sharpes "The Carp" has it on the ferrules as well.
Jim Somers told me it was done to help stop wear from silk lines. As the ferrules bulge out a little, the silk line could rub against the whipping, thus cutting the thread in time. The wire naturally would not do this. Same with the butt ring as the line can bunch up as it flows through.
I think..but am not too sure, that i may have some of the original wire left from when I helped build/repair rods for Jim all those years ago.