UPDATE: FOR REASONS THAT YOU'LL SEE IF YOU READ THE COMMENTS SECTION, THIS WHOLE IDEA TURNS OUT TO BE A BIG PILE OF DOGGY-DO. MY APOLOGIES. I LEAVE THE POST UP ONLY AS A MEMENTO OF MY STUPIDITY.
But if we really wanted all MPs to have more than 50% of the vote, even under First Past the Post, it would be quite simple:
If a constituency gives no candidate 50% support, then that constituency doesn't return an MP.
(Note that this approach wouldn't work under AV, since at least one candidate always gets more than 50%.)
It's a radical approach, but it has its pros and cons. The main pro is that it is something that would really encourage candidates to seek a broad base of support. The con is that it would leave many (perhaps most) constituencies unrepresented.
Under FPTP, and under AV, we do have a mechanism to indicate that we don't want any of the candidates to represent us at Westminster - we don't vote. At the last general election, 35% of the UK took that option, more than the fraction who voted for many of the winning candidates.
The problem is, there's more than one reason for abstention. It may be to wish a plague on all their houses, or it may be because we couldn't be bothered, or were away on business, or whatever. We can demonstrate that we really do care enough to go to the polling station, by turning up and then spoiling our paper, but even then there is no way to distinguish between the conscientious abstainer and those can't tell the sharp end of the pencil from the blunt one.
What we need is a genuine box in which to put our cross, labelled NOTA - None Of The Above.
Would it have much effect? Perhaps not.
Under FPTP, the NOTA votes would be counted and would certainly be of interest if NOTA came in third or second or even (dare we hope?) first place. But it wouldn't actually make any difference.
Under AV, NOTA would have less impact. The winning candidate would still get over 50% (it can't be avoided). If a voter put NOTA as their first choice, and then listed the other candidates, then they would be saying, 'I don't want any of these candidates, but if I have to have one of them, here's my order of preference.' Well, the fact is you do have to have one of them, and so your NOTA vote would instantly be dismissed and the process would carry on as normal with your second-choice vote being counted.
But what if, as suggested above, you could have none of them? What if, under FPTP or AV, NOTA was counted like any other candidate and could win. It would be rare I think, but it's an option that would allow voters to truly express themselves. Under FPTP things would be, inevitably, simple. If NOTA gets more than any other candidate then NOTA wins and the constituency returns no MP.
Under AV things are (inevitably) more interesting. The NOTA selection could go anywhere in the list that the voter chooses - top, bottom, or middle. And suppose you list the candidates in the order A, B, C, NOTA, D, E , F. That would be saying, 'I'm happy to have A or B or C as my MP, and of them, here's my order of preference. I don't want any of D, E, F, but if it comes to it, I do still have a order of dislike.'
That's really quite expressive. Under standard AV, however much you loathe and despise candidate F, you still have to list them to get the most of you vote, you put them last, seemingly suggesting that you would like them to be your MP, just that you'd like others more. By putting that NOTA break in there, you're effectively producing one list of candidates you like and another of candidates you don't, and putting the BNP (sorry, candidate F) at the top of that list. (It has to be said that this is a point of perception, not something that directly effects the result, but perception is important.)
There's still one problem, however. In a constituency where NOTA wins, the people don't get a representative in Parliament. The best I can come up with is that the runner-up gets forced to go to Westminster, but doesn't get a salary. I can see the fairness of it, but I can also see how it might produce an MP who slightly less than enthusiastic about their job - which was really the whole motivation for electoral reform.
But that's a detail. The important thing is to modify AV by adding this NOTA option. So who's with me? Who will make their voice heard? Who will climb up onto the roof tops and shout out the slogan to all who will listen:
'Vote NOTA-AV!'