Catholic Archbishops, Vincent Nichols and Peter Smith, are guilty of misleading the faithful - either deliberately or by careless omission. Last Sunday, they instructed every Catholic parish priest in England and Wales to read out a letter to the congregations of 2,500 Catholic churches.

The Pastoral Letter On Marriage, signed by the archbishops, opposed government plans to legalise same-sex marriage; suggesting that it was the moral "duty" of all Catholics to fight plans for marriage equality.

Mischievously, their letter did not make it clear that the government was proposing to allow gay couples to marry only in a civil ceremony in a register office - not in places of worship. Whether by intention or default, the fact that churches would not be forced to conduct same-sex marriages was not made clear.

As a consequence, many Catholics left church last Sunday believing that the government was going to compel priests to marry lesbian and gay couples.

I know this because after Sunday Mass I interviewed people coming out of London's premier Catholic church, Westminster Cathedral. Three quarters of the people I spoke to were under the impression that the archbishops were talking about same-sex marriages in churches. They thought the government was going to force unwilling religious institutions to marry same-sex couples. This is untrue. The planned legislation will apply to civil marriages in register offices only.

Perhaps the archbishops should now acknowledge the confusion and misunderstanding they have created. An apology and clarification might be in order - and appreciated. Deception is not a Christian value. An inadvertent deception that is not corrected is equally un-Christian.

It is very rare for senior clergy to write a Pastoral Letter and require it to be read out in every Catholic church in the country. Such letters are normally reserved for major, exceptional occasions.

It is therefore rather odd for the archbishops to conclude that blocking gay marriage is so important that it merits a Pastoral Letter being read to every parishioner during mass.

Given the many huge life and death problems in the world - war, hunger, poverty and dictatorship - it seems somewhat bizarre that Catholic leaders have chosen to focus on gay marriage for their great crusade. This strikes me as evidence of skewed moral priorities.

Despite the moderate language of their letter, the archbishops are, in essence, preaching a gospel of division and discrimination. They want to divide gay people from straight people. In their view, the law should discriminate against same-sex couples by denying them equal marriage rights.

Pardon? Discrimination is not, as far as I know, a Christian value.

If the church genuinely supports love and commitment, why does the Catholic hierarchy oppose gay couples showing their love and commitment by getting married? It doesn't make sense.

While the Archbishops preach the virtues of marriage they simultaneously want to exclude people from participating in it. On the one hand they encourage and venerate marriage and on the other hand they seek to deny its benefits and graces to couples who happen to be of the same-sex.

If the faith organisations recommend marriage and believe we should all aspire to be married, why bar lesbian and gay couples?

The archbishop's letter includes no acknowledgement of the profound love that can exist between two people of the same sex. It wilfully ignores that fact the gay marriage is about love. By opposing marriage equality, the archbishops are denigrating, demeaning and devaluing love between two people of the same sex. It's an insult - a slap in the face - to loving, loyal and long-term lesbian and gay relationships.

Given the archbishops support for the institution of marriage, surely they should welcome the many lesbian and gay couples who want to get married?

Opening up marriage to same-sex partners does not detract one iota from heterosexual marriage. It causes straight couples no disadvantage or diminution of their rights.

In a democratic society, Catholics (and others) are entitled to believe that same-sex marriages are wrong, but they are not entitled to demand that their opposition to gay marriages should be imposed on the rest of society and enforced by law.

Allowing religious organisations to veto legislation - which is what the archbishops are demanding - is the path to theocracy.

The church has no legitimate reason to block same-sex civil marriage ceremonies. What happens in a register office is not the business of the church. It is outside their jurisdiction.

Regardless of what the archbishops may want, the case for marriage equality is overwhelming and inevitable from a democratic and human rights perspective.

As well as pushing the government to end the gay marriage ban, the Equal Love campaign is pursuing a legal case.

We are seeking to open up civil marriages to same-sex couples and civil partnerships to opposite-sex couples. Our goal: full marriage and partnership equality, without any discrimination based on sexual orientation.

In February 2011, four gay couples and four heterosexual couples, sponsored by the Equal Love campaign, filed a historic joint appeal to the European Court of Human Rights (ECHR).

Our appeal argues that Britain's twin legal bans on same-sex civil marriages and opposite-sex civil partnerships amount to illegal discrimination, contrary to the European Convention on Human Rights. The bans violate Articles 8, 12 and 14 - respectively the right to privacy and family life, the right to marry and the right to non-discrimination,

Even if the archbishops succeeded in intimidating the government and parliament to pull back from legislating equal marriage rights, we will win in the courts.

The Catholic Church, and other homophobic institutions, should adjust to reality with good grace, rather than resist the inevitable and be seen as old fashioned bigots. Marriage equality is an idea whose time has come - and no dogma can stop it.

* Further information about Peter Tatchell's human rights campaigns and to make a donation: www.PeterTatchellFoundation.org