This paper describes the preparation and the electrical and physical characterisation of solid electrolytes of the form Me(x)-Bi8Pb5O17+y, where Me is a metallic dopant, either Ni or Cu. Doping with Ni produces single phase mixed ionic/electronic electrolytes with ionic conductivity comparable to that of the undoped material. The ionic transference number (t(i)) of the Ni doped material can be tuned between 0.5 and 0.9 by varying the Ni concentration. Nickel can significantly improve the mechanical properties required for the production of leak-tight membranes. Copper doping produces a two phase material with mixed ionic/electronic conductivity.