John Curtice: New politics? More like an old-fashioned political fix

ELECTIONS to the Commons play two roles. They provide voters with an opportunity to choose their local MP. And they give the country as a whole the chance to decide the next government.

In advocating a switch to the Alternative Vote, Mr Brown is focusing on the first of these two roles. He argues that, because it ensures every MP has to secure the expressed support of at least half of the voters in their constituency, the system would help to restore the tattered bonds of trust between MPs and the public.

But its adoption could potentially have important implications for who enters 10 Downing Street. If a party can consistently pick up a lot of second-preferences, it is likely to win more seats.

The Liberal Democrats are often everybody's second favourite. But such second preferences are useful only if a party is already a close second. This is only occasionally true of the Liberal Democrats – though Edinburgh South is a notable exception. On the party's current standing – 18 per cent or so – second preferences would probably deliver it a dozen or so extra seats.

The SNP is unlikely to gain much either. The Nationalists cannot be sure of winning more second preference votes from Conservatives and Liberal Democrats than Labour. They only have one good second place, Ochil, anyway.

But who do Liberal Democrat and SNP voters prefer more – Conservative or Labour? The answer is clear – Labour. In the ICM poll, 45 per cent of Liberal Democrat supporters said Labour was their second choice, only 28 per cent the Conservatives. Only a handful of SNP supporters in the 2007 local elections gave any support to a Tory candidate.

So where Labour lie a close second to the Conservatives, the new system could enable them to capture the seat. But the Conservatives are unlikely to gain where they are close to Labour – while of the two parties they are also more likely to be leapfrogged by a local Liberal Democrat.

Overall, the ICM poll suggested the new system could cost David Cameron's party some two dozen seats, while Labour would be around a dozen or so better off.

Under current circumstances at least, the attractions of the Alternative Vote for Labour are clear. Its adoption would make it even more difficult for the Conservatives to win a majority, only make it a little easier for the Liberal Democrats to secure extra seats, while Labour's chances of winning a majority might even be enhanced.

Not so much "new" politics as an old-fashioned political fix.

• John Curtice is Professor of Politics, Strathclyde University