LONDON (Reuters) - Hoping to align religious tradition with modern life, the Church of England has introduced a new “two-in-one” marriage and baptism ceremony that allows couples who already have children to tie the knot.

“Family-friendly weddings” will make it easier for those with children to marry in church, the Church of England said on Thursday as it launched an appeal to cohabiting couples in an increasingly secular Britain. If successful, it would also mean more young people being baptised into the Church.

The decision follows research showing that one in five couples in Britain who get married in church already have children. But critics say such a move condones sex before marriage and will reinforce the trend towards cohabitation.

“This is a response to the demand that is on us as a church to meet people who come to us for this key event in their lives,” said a Church of England spokesman.

While the Church, fighting to retain numbers, seeks to attract worshippers with a more flexible and modern approach, some clergy say the move breaks with traditional ethics.

“It is a huge mistake. You cannot have the two-in-one, they do not go together,” said retired Reverend Beverley Thompson.

Thompson, who took early retirement from the Church of England after the ordination of female priests in 1994, said it destroyed the distinct sacraments of matrimony and baptism.

“That really is giving the okay to cohabiting,” he said. “It is an attempt to meet people where they are, but the Church has to serve people not on their terms but on God’s.”

The Church of England said it was not condoning sex before marriage but giving people the option to celebrate their lives, and those of their children, in a more relevant way.

“We are not changing our teachings. It is not something that should particularly contradict views of traditionalists,” said a spokesman for the Church, which has about 1.7 million regular worshippers, but which has seen Sunday church attendance in Britain decline sharply over the past decade.

The two-in-one ceremony costs about 300 pounds ($500) -- little different to the cost of holding the ceremonies separately.

But it offers the chance of large savings on celebrations, avoiding the need to hold two separate events, the possible hiring of two venues and sets of caterers.

“It is more convenient, more environmentally friendly with people just making the journey once,” said a Church spokesman.