Hundreds of priests have signed an open letter urging the Pope and the Church to stand firm on traditional teaching on marriage and homosexuality.

The letter, published in the Catholic Herald, is significant because the province of England and Wales is regarded as one of the more liberal provinces in the worldwide church. For nearly 500 priests in the UK to make such a gesture is an indicator of the depths of concern in the Catholic Church about liberalising trends.

The letter also shows the early drawing up of battle lines as different factions of the Church prepare to go to war in Rome in October over where the lines should be drawn on offering Communion for those who are divorced and remarried, and on homosexuality.

The letter calls on those attending the coming Synod on the Family, which will conclude the consultation process begun last October, to issue a "clear and firm proclamation" upholding Church teaching on marriage.

The priests write: "We wish, as Catholic priests, to re-state our unwavering fidelity to the traditional doctrines regarding marriage and the true meaning of human sexuality, founded on the Word of God and taught by the Church's Magisterium for two millennia."

Retired German Cardinal Walter Kasper is among those who believe divorced and remarried Catholics should no longer be barred from receiving Communion.

The 461 priests from England and Wales say this must be resisted.

They write: "We affirm the importance of upholding the Church's traditional discipline regarding the reception of the sacraments, and that doctrine and practice remain firmly and inseparably in harmony."

One signatory told the Herald that there "has been a certain amount of pressure not to sign the letter and indeed a degree of intimidation from some senior Churchmen."

Another said: "Mercy requires both love and truth. There's a lot at stake. Not all priests would be comfortable expressing themselves in an open letter, but I'd be very worried if there were priests who disagreed with the sentiments it contains.

"The letter calls for fidelity to Catholic teaching, and that practice should remain 'inseparably in harmony' with doctrine. The priests state that they remain committed to helping 'those who struggle to follow the Gospel in an increasingly secular society', but imply that those couples and families who have remained faithful are not being adequately supported or encouraged."

Neither was prepared to be quoted by name, but prominent signatories include theologians such as Fr Aidan Nichols and Fr John Saward and Oxford physicist Fr Andrew Pinsent.

According to one leading Catholic blogger, on The hermeneutic of continuity site, there is a growing suspicion that the Synod will unleash division in the Church by attempting to re-shape Catholic teaching and practice to accommodate modern ways of living and thinking about relationships and sexuality.

The letter reads: "Following the Extraordinary Synod of Bishops in Rome in October 2014 much confusion has arisen concerning Catholic moral teaching. In this situation we wish, as Catholic priests, to re-state our unwavering fidelity to the traditional doctrines regarding marriage and the true meaning of human sexuality, founded on the Word of God and taught by the Church's Magisterium for two millennia... We urge all those who will participate in the second Synod in October 2015 to make a clear and firm proclamation of the Church's unchanging moral teaching, so that confusion may be removed, and faith confirmed."