If there had been AV in 2005

Over on the BBC's website John Curtice has calculated what the results of the last 6 elections would have been had the Alternative Vote been in use. The projections are based on the British electoral studies between 1983 and 1997, and ICM polls from the 2001 and 2005 elections.

Curtice projects that in 2005 the Alternative Vote system would have given Labour 21 more seats, the Lib Dems 6 more and the Conservatives 27 less. Generally speaking, Curtice projects that the system would help the Liberal Democrats, and punish the second placed party. The most drastic effect would have in 1997, when he suggests it would have resulted in the Conservatives losing an extra 95(!) seats, and the Lib Dems gaining an extra 69 - giving them more seats than the Tories overall.

These are, of course, quite rough calculations since they assume people would still cast their first preference votes in the same manner

In 2005 Conservative voters would have split their second preference votes 54% Liberal Democrat, 21% Labour and 15% other. Labour voters would have split their votes 59% for the Lib Dems, 22% for the Conservatives and 11% for others. Lib Dem voters would have split 54% for Labour, 26% for the Tories and 11% for others.

While the Conservatives have increased in the polls, these figures haven't changed massively since 2005. ICM asked a the same question in 2008, and the second preferences of Lib Dem voters were then CON 28% (up 2 since 2005) and LAB 45% (down 9 since 2005).