There is strong evidence that voting behaviour is both ends-directed and rational. That is, electors choose to vote because of the effects their vote will have, and do not vote if these effects are insufficient to outweigh the costs of voting. However, as Downs’ paradox shows, rationality and egoism together imply non-voting. The evidence suggests that egoism is the postulate which must be abandoned. . . . voters’ interest in political information increases with the importance of political choices. Once again, this is consistent with rationality but not with egoism.
Our article had more math and more focus on U.S. politics but the basic point is the same.
Also let me use this as yet another excuse to plug a wonderful article, The Norm of Self-Interest, by psychologist Dale Miller, in which he argues the following:
A norm exists in Western cultures that specifies self-interest both is and ought to be a powerful determinant of behavior. This norm influences people’s actions and opinions as well as the accounts they give for their actions and opinions. In particular, it leads people to act and speak as though they care more about their material self-interest than they do.