There is apparently to be a statement today by Gordon Brown about constitutional reform, which will include proposals for exploring voting reform by the so-called "National Council for Democratic Renewal", which is not a national council at all but just a committee of Ministers of the government.
Some on the right have regarded this as a last act of desperation by the Prime Minister in order to keep Labour in power. There is probably some force in this given that his initiative comes on the heels of a historically poor performance by Labour in the county and European elections last week. If that is not Gordon Brown's real purpose then it gives us another example of his inability to read how his actions appear to the world outside, because most will perceive his motives to be suspect.
The Liberals may feel that this is their big opportunity to pursue proportional representation. Proportional representation is good for any small party which can place itself as a party of the centre, because it would result in a string of coalition governments, and a party of the centre forms the obvious coalition partner for two larger parties with more opposed political leanings such as the Conservatives or Labour. The Liberals could expect to be in power as junior partners for a number of years - that is, until new political groupings were to emerge as politics splinters, as in due course it would and does under proportional representation.
However, rather than proportional representation, the only form of voting reform which it appears that the Prime Minister could get through his own cabinet is some kind of single transferable voting system, sometimes also called alternative voting because this system allows a voter to choose an alternative candidate should her main choice (first preference) be knocked out because of a lack of first preference votes. Full-on single transferable voting enables subsequent transfers to third and fourth preferences and so on should earlier preferences be knocked out, but this is something of a purists' refinement which has little practical impact. However it is implemented, it is not proportional representation; but some right wing commentators still see it as a devious plot by the Prime Minister to keep the Conservatives permanently out of power.
I think this is a misreading, or at least an exaggeration. Boris Johnson was elected Mayor of London under this system in 2008 in an area (Greater London) which historically is by no means friendly to the Conservatives, and he only received marginally less second preference votes than did Ken Livingstone, and at a time which was uninfluenced by the MPs' expenses scandal. Such limited polling evidence as there is suggests that just at present the Conservatives would gain more second preference votes from Liberal supporters than would Labour. This is not surprising given Labour and Gordon Brown's current unpopularity, but unfortunately there is little reliable evidence on the trends over the long term. One suspects Liberal voters may on average be slightly more attuned to Labour, but I also suspect that second preference support turns more to whoever is in opposition at the time. What it is likely to cause is a greater difficulty for a government in winning a second term, as it amplifies movements of political opinion amongst floating voters.
There is one further thing to be said about alternative voting: it has great dangers for the Liberals. It encourages the smaller specialist parties such as the Greens or UKIP as first preference one-issue "pressure groups", leaving voters secure in the knowledge that their vote will not be wasted because they can specify Labour or the Conservatives as their second preference. In the round, this would tend to reduce the vote for the Liberals rather than increase it.
The big losers of voting reform could well be the Liberals, and the gainers the one-issue pressure groups who would be given a platform. Be careful what you wish for.