A very brief further Bonkers Electoral System Update. I had forgotten (or never noticed) that the Jenkins Commission considered PFPTP, calling it ``the `weighted' vote'', but rejected it on the grounds that,
... there would be great problems if one of these vote-heavy beasts [an MP from a party underrepresented in the Commons, i.e., one who would have a relatively large voting weight under PFPTP] were to find himself in a lobby different from his party leader and whips, or worse still, if he were permanently to lumber off across the floor. There would inevitably be the most excited attempts to re-corral him. And the ability sometimes to take independent action must surely be preserved, even encouraged, if MPs are not to become party automata.
Therefore, while we respect the ingenuity and conviction with which this weighted vote solution has been put forward, we think that it would arouse more mockery than enthusiasm and be incompatible with the practical working of a parliament.
Suppose you are a political party and you have -- let's say -- 356 MPs in the Commons. Suppose further that one of these MPs considers rebelling or defecting. This makes a difference of one 356th to your power in the Commons, whether under the current FPTP system or under PFPTP. For party whips and leaders, PFPTP makes no difference to the consequences of and incentives for preventing rebellions.
It could make a difference in how different parties court MPs who intend to cross the floor; for instance, suppose that you are (say) the Liberal Democrat Party and you know that a Labour and a Conservative MP are each considering defecting to your party, but that neither will defect if the other does. If all that matters to you is votes in the Commons, you would obviously prefer the Tory to defect, since -- at the moment -- under PFPTP Tory MPs would have a larger voting weight than Labour; and so you would encourage them to desert at the cost of preventing the other from doing so. But defections are in any case uncommon and I don't believe that parties evaluate them purely in terms of their effect upon Parliamentary arithmetic.