In reply to John Kay:
Strange, though, this was probably because the original sole units are no longer available. However, you able to call in? I called in on the way home from the Lakes back in January, and, after looking at my boots they produced two alternative, though similar, Vibram unit that would fit; one pair with heel and toe welts for step-crampons, the other without. I did have to wait though, their lead in time being around three months! Very pleased with the result though.