I HAVE been wondering what it is that drives us to vote the way we do. I have my prejudices, and there is a certain party I would find it hard to vote for. This is not a rational reaction, but a visceral one; a question of basic loyalties that are very hard to shake off.

Politicians know this, of course, and try to tap into those gut beliefs which inspire the core of their party followers. We even talk about the "party faithful", as if they were members of a sect. There is something Manichean about the conviction that salvation lies on only one side of a political divide, and that total disaster lies ahead if the other lot get in.

Experience, however, suggests that the most interesting politicians are those who have the capacity to reach out and intrigue people whose gut instincts are on the other side. This is what Margaret Thatcher did to aspirational working-class voters, and what Tony Blair did to the anxious middle classes. I suspect that much of the odium in which those two party leaders are now held goes back to the fact that some at least of their "party faithful" believe that they betrayed their parties' deepest instincts. Not only that but, by reaching out beyond party lines, they encouraged others to a similar betrayal.

But perhaps treachery of this kind is not the gross disloyalty that it appears to be. It could actually be a political virtue. Think of Winston Churchill, who crossed the floor of the House of Commons in 1904 (from Conservative to Liberal) and crossed back again in 1924. It takes nerve to admit the tug to the heart and mind of the other side's concerns, and real courage to admit that the opposition might have some good ideas. By their capacity to think independently, "treacherous" politicians explode the Manichean trap: the all-too-cosy notion, beloved by political as well as religious fundamentalists, that there are only two sides, and that one is evil and the other is good.

It is this that I am struggling with as I prepare to vote. My inner Manichee does not know which way to jump, and the result is that I still don't know quite where I am going to put my cross next Thursday. There is, of course, no box for the "traitors", because they all pretend loyalty at election time (though no doubt they will emerge with a vengeance if the result requires the brokering of a new coalition). I can only hope that the outcome will include some genuine surprises; that we will discern providence, and even humour, when we wake up next Friday morning.

The Revd Angela Tilby is Diocesan Canon of Christ Church, Oxford, and Continuing Ministerial Development Adviser for the diocese of Oxford.