According to a study summarized in the Times Online:
Cleverer children are more likely to vote for the Green Party or the Liberal Democrats in a general election than other parties when they become adults, research suggests. The study, by the University of Edinburgh and the UK Medical Research Council and published in the journal Intelligence, indicates that childhood IQ is as important as social class in determining political allegiance. The IQs of more than 6,000 subjects were recorded at the age of 10, before any secondary schooling. Twenty-four years later they were asked about their voting habits.
(Thanks to Babette Hogan over on Facebook for posting this item)