For the first time, the leader of the Roman Catholic Church in England and Wales has told worshipers to bombard MPs with letters to lobby them to vote against introducing same-sex marriage.

Vincent Nichols, the Archbishop of Westminster said he wanted politicians to “resist the proposed redefining of marriage with all its likely consequences particularly in schools and in how children are taught about the “true nature of marriage”.

In a letter read out in churches on Sunday, he said: “At this time, we look to our Members of Parliament to defend, not change, the bond of man and woman in marriage as the essential element of the vision of the family.

“I urge everyone who cares about upholding the meaning of marriage in civil law to make their views known to their Members of Parliament, clearly, calmly and forcefully. Please do so as soon as possible.”

Christmas, he wrote, was “a time in which to speak up for marriage, between a husband and a wife, as the heart of the family”.

He said society needs “a clear vision of marriage and family, based on human nature itself”.

“The vocation of marriage”, he said is“rooted in a natural bond, blessed by God”.

Also on Sunday, a letter from the Archbishop of Birmingham, the Most Reverend Bernard Longley was read to parishioners in Birmingham. His letter said: “Government policy cannot foresee the full consequences, for the children involved or for wider society, of being brought up by two mothers without a father’s influence or by two fathers without a mother’s influence.

“We first learn about diversity and acquire a respect for difference through the complementarity of our parents.”

The letter continued: “The complementary love of father and mother is a precious gift that we should wish for every child.

“We know that many single parents courageously and generously look after their children and often struggle to give them a fine upbringing.

“If it had not been for the understanding of St Joseph, our Lady herself might have had to face the difficulties of being a single parent.

“Even so, the experience of growing up with our father and mother to teach and guide, to console and love us unconditionally is an invaluable blessing in life.”

On Christmas Day, the Archbishop of Westminster said: “here was no announcement in any party manifesto, no green paper, no statement in the Queen’s speech.

“And yet here we are on the verge of primary legislation. From a democratic point of view, it’s a shambles.

“George Orwell would be proud of that manoeuvre. I think the process is shambolic.”

The archbishop ignored the fact that the governing Conservative Party included a commitment to begin the process that has lead to the plans for equal marriage.