Investigations with respect to proposals for government intervention generally deal with values, ideologies or strategies of party leaders. Theoretical studies predict that, in an environment where information is imperfect and costly, politicians have incentives to formulate interventions, the benefits of which are concentrated while their costs are diffused. The authors elaborate a theory of supply of government intervention which predicts the characteristics of interventions that increase the number of votes as well as the characteristics of actions that lead to vote losses. The predictions of this theory are tested by using the proposals for government intervention in the official programmes of the political parties of Quebec during the 1960–1981 period. The two basic findings are that (1) the prediction relative to the anti-consumer and anti-taxpayer bias of the political market is not supported by the facts, and that (2) the party leaders prefer to finance the cost of their proposals of government intervention through the mode of fiscal illusion instead of hoping for inattention on the part of consumers and taxpayers.