The Economist has this article about the upcoming British vote on Instant Runoff Voting (called Alternative Voting in Britain, or “AV” for short). Toward the end of the article, one reads that the University of Essex studied exit polls and opinion polls from the last election, and predicted what would have happened if Britain had been using IRV in that election.
The actual results were: Conservative 305 seats, Labour 258 seats, Liberal Democrats 57 seats (the article doesn’t mention the seats won by other parties). Under IRV, the study predicts the results would have been: Conservative 283, Labour 248, Liberal Democrats 89. Thanks to Jerry Kunz for the link.