AV voting referendum: Alan Renwick's viewpoint

Both sides have exaggerated the merits of their systems, he says

A referendum will be held on 5 May on whether to keep the first-past-the-post system for electing MPs or to switch to the Alternative Vote. The BBC is asking a variety of people to give their personal view.

"The Yes and No campaigns for the coming referendum are spinning furiously.

Unfortunately, most of the arguments offered on both sides are either exaggerated or outright false.

The No camp asserts that the Alternative Vote (AV) system gives extra votes to supporters of fringe parties. This is simply untrue.

In each round of counting under AV, every voter has one vote and one vote only. They say that AV would require expensive voting machines. Again, that is just plain false.

The Yes side tries to avoid such blatant falsehoods, but its supporters sometimes get carried away.

Lord Ashdown recently claimed that AV would eliminate safe seats. No it wouldn't: the number of safe seats would be cut a bit, but many would remain.

There is no reason to think AV would have prevented abuse of the MPs' expenses system.

Finely balanced

In fact, the real arguments are finely balanced. Two points favour AV. First, it allows voters to express their views more fully. Few of us today are rigidly attached to one party. Under AV, we can express our nuanced preferences.

Second, AV is more likely than first-past-the post to yield a fair result at constituency level.

Under first-past-the-post, a candidate's success depends partly on their popularity and partly on how many other similar candidates are running.

In a constituency with one candidate from the left and three from the right, the left-winger could currently win even if right-wing voters are in the majority, because the right-wing vote splits. That is much less likely under AV.

But there is also an important argument against AV.

At the national level, it makes the sort of result that British voters favour a bit less likely. Most of us - rightly or wrongly - like single-party governments with moderate rather than landslide majorities.

But AV slightly increases the chances of both hung parliaments and landslides.

Whether you support change or the status quo should depend on which of these points you think matters more.