The Danish parliament uses plurality voting; the Finns and Swedes opt for serial voting; the Norwegians have provision for two-round voting. Sadly, even when the question isn’t binary – and Brexit is definitely not binary – Westminster still relies on binary ballots.
A binary ballot may be ‘meaningful’ if and when there are only two options. When there are three or more options, however, it might mean next to nothing. Consider a hypothetical debate on five options – A, B, C, D and E – in a parliament of 100 MPs with the following imaginary levels of 1st preference support:
A majority vote – “A, yes-or-no?” “B, yes-or-no?” etc. – could be ‘meaningless’ as there are majorities of 70%, 90%, 75%, 80% and 85% against each. There’s no majority for anything.
A different majority vote – “A or B?” “A or C?”… “B or C?”… “C or D?” etc.; there are ten such pairings altogether – could give one of four different outcomes: A, C, D or E. Again, therefore, any outcome could mean not very much.
Political leaders like majority votes. In parliaments or in referendums, they choose the question and, usually, the question is then the answer. Mrs May is now ‘disguising’ her “C, yes or no?” vote (which she could again lose) as a “C or E?” vote (which she might win). But logically, any conclusion that such a ‘25:15’ majority result, now ‘disguised’ as, say, 55:45, represented “the will of parliament” would be ‘fake’.
In contrast, preferential voting would produce an outcome which was accurate and ‘meaningful’. Such an outcome might be the 1st preference of few but, if it were the 2nd or 3rd of umpteen, then maybe it would indeed get the highest average preference score. Such preferential voting is a “best interpretation of majority rule,” (Oxford Concise Dictionary of Politics), and should be the basis of parliamentary decision-making.