What is a conscience? This is the question Brown opened when he said that "exercising your conscience will mean for Labour Party members a free vote" on parts of the embryology bill.
But, as Janine asks, why should conscience only permit a free vote here? To take just one example, many Labour MPs consciences might - or should - stop them wanting to put people in jail for 42 days without charge. But there's little hope of a free vote on the Counter Terrorism bill.
What Brown means by "conscience", then, is "religious belief." Which raises the question: why should religious beliefs have a special status in politics that allows MPs free votes when they don't get them on other grounds?
Now, I'm by no means as hostile to religion as some, but I have three problems with this:
1. It treats the consciences of religious believers with a respect not given to those of agnostics.
2. It gives too much respect to religious loyalties over others. It takes for granted what should be questioned - that one's loyalty to one's church should over-ride one's loyalty to one's party. But why should this be the case when - to take our 42 days example - loyalty to liberal principles is not given similar status?
3. It privileges some forms of moral thinking over others. Why should a belief founded (perhaps loosely) in religious doctrine entitle an MP to a free vote when beliefs - which might be much more rigorously considered - founded in secular moral philosophy do not?