Priests make bad politicians. Do the cardinals and bishops of the Roman Catholic Church realise what a hornets' nest they are stirring up when they say that Roman Catholic MPs should follow the church's teaching when voting on abortion? They are messing with the democratic process - and Roman Catholic MPs could pay the price.

We have all heard the emotive language and denunciation handed out by Cardinal Keith O' Brien and supported by his fellow bishops in England and Wales. Catholic MPs who support legalised abortion should abstain from communion, they say. That is a serious matter for people of faith. What happens if a sizeable number of these MPs are cowed into submission? They are, after all, only human. How will the electorate react if it notes a corresponding change in policy?

Forty one million people in the UK identify themselves as Christian but only one-tenth of this number is Catholic. Under Labour it is possible that there is a higher representation of Catholics in the House of Commons than in the population at large. If their church is thought to dictate their voting patterns, how long will it be before MPs will have to declare publicly their religious affiliations? And if the Catholic church is known to lean on Catholic MPs, what chance will any Catholic have of being elected?

Only the most bigoted voter currently approaches the ballot box with any knowledge of or interest in the religious faith of their chosen candidate. We vote for a parliamentary representative because we think the policies his or her political party espouses best represent our own views. But if this policy continues, a candidate's religious belief will need to be openly declared before we place our X in the box.

In fact, if the Roman Catholic Church, or any other, wants its deeply-held beliefs to be instrumental in shaping the laws of the land - in other words to exercise political power - it had better openly field its candidates and publish its manifesto. We could expect an immediate end to legal abortions. This might be followed by a ban on contraception and a curtailment of gay rights. Divorce would probably be outlawed and the church would have a strong input into education.

The approach would have the virtue of honesty and transparency. And when the votes were counted, the church would have an exact measure of the extent (or want) of democratic support for its views. What it cannot and should not do is to attempt to impose its will by the back door. It is wholly improper to pressure MPs who have been elected regardless of, not because of, their private faith.

What a precedent might this ploy set if we had a strong Islamic constituent in the Commons? Could we expect the creep of sharia law?

Abortion is such a sad and emotive issue. It is so sensitive and so personal that MPs are released from the restriction of the party whip when they vote on it. What they are not released from is the moral requirement that they answer to the people they represent. They are not passing through the lobby on behalf of the Pope, archbishop, imam or rabbi but on behalf of the people who put them there.

And when those MPs vote in favour of legalising abortion, aren't they simply recognising that the issue is so complex and so important that the ultimate decision should be left to the conscience of the person most closely involved - the mother of the unborn child. It is she alone who has to weigh the difficulty of bringing a child into the world against the pain of denying it life.

I have never been unfortunate enough to be confronted with a crisis pregnancy but I know several women who opted to abort. In all but one case the short procedure triggered years of grief. And yet all but one of these women say they would have to make the same decision again.

As someone who was born a Catholic, I was taught at my convent school that clear blue water must lie between church and state. There was also a lesson from the New Testament which seemed to me to emphasise the point. In it Christ said to "give unto Caesar that which is Caesar's and unto God that which is God's". The sanctity of life, many will argue, lies in God's realm. But law-making, in our secular society, lies within the realm of the state. Long may it remain so.

The princes of the church are saying that if a Roman Catholic MP supports the legalisation of abortion, he should cease to take communion. To appreciate the pressure this exerts on those parliamentarians, it's necessary to understand that if a Catholic commits any sin, however heinous, and repents and confesses, he or she could take communion two minutes later. Forgiveness is at the core of the religion. These draconian statements sound unforgiving, almost unChristian. We did not hear such outspoken condemnation even when the paedophile priests were exposed. Yet to legalise abortion is not necessarily to believe it to be morally correct. It is simply to recognise the right of each citizen to reach an individual decision about whether to carry a pregnancy to term, guided by their individual conscience, without breaking the law.

Abortion is illegal on the island of Ireland. North as well as south of the border, women who find themselves with an unwanted pregnancy have an enforced cooling-off period - of the sort Cardinal Keith O'Brien would like to see here - though for different reasons. Between diagnosis and termination they must organise the loneliest journey of their life. I don't suppose the research exists to determine just how many hundreds of thousands (maybe millions) of plane and ferry journeys have been clocked up on the termination trail to Scotland and England. But it is a well-worn path - testimony to the fact that even the combined efforts of church and state will not stand between a woman and her decision to abort.

Although the church has opposed abortion since the second century, Catholic countries, even where it is illegal, have high levels of abortions. In Brazil, estimates range from one million to two million per year, and in Peru 5% of women of childbearing age have abortions each year, compared with 3% in the US.

Why are there so many? You would have to ask each woman for her story. But I would say this: Cardinal Thomas Winning instituted a scheme that offers financial support to pregnant women who keep their baby. It is a benign, intelligent and compassionate initiative that made the headlines because of its rarity.

If this church or any other church wants to encourage women to go through with their pregnancies and keep their children, they would do well to rethink their objections to contraception and to offer mothers and mothers-to-be open-hearted and open-handed support. They would do even better to lecture, for a change, the men under their spiritual charge. Let them speak to the fathers; to demand that they support, emotionally and financially, the children they beget in and out of wedlock, by mothers they impregnate above and below the legal age limit, by means fair and foul.

Meantime, let them cease their attempts to bully those elected to shape the country's laws, who also happen to be Catholic.