Cable is not a man without vanity and he must know that, being a Liberal Democrat, the Speakership is the highest office realistically available to him. The history books will not likely remember the shadow shadow Chancellor, but might well celebrate the Speaker who restored the Commons’ dignity.
Personally, I think Frank Field would probably be the best choice. But Cable is the only candidate who by merely being dragged to the chair would boost the public’s respect for Parliament. Cable is well enough known and respected that his elevation would have an instant effect.