"The great experiment to downplay marriage" has "clearly failed", the Bishop of Lichfield has said in a pastoral letter published in the March editions of parish magazines in the Diocese of Lichfield.

In his letter, the Rt Rev Jonathan Gledhill hit out at the erosion of marriage's unique status as cohabiting continues to gain greater acceptance.

He points to the recent British Social Attitudes Survey which found that 66 per cent of the population regard marriage and cohabitation as being on an equal footing.

"But are they right? Is deciding to get married or not just another personal choice, like whether to drive a Ford or a Vauxhall?" he asked.

Bishop Gledhill called for a greater distinction between marriage as a union between a man and a woman, and civil partnerships between same-sex couples.

"Most of my gay friends would want to distinguish between marriage, which is something that happens for a man and a woman, and a civil partnership, which allows you to be committed together in a kind-of household for life with your gay partner," he said.

"I think I'd want to make a distinction. It's a bit careless to call it marriage, in other words."

Bishop Gledhill warned of the risks to children posed by the increasing normalisation of cohabitation, saying, "Our children deserve the chance to be brought up by a man and a woman who promise to love each other always."

He went on to acknowledge that many marriages are far from perfect, but stressed that the heart of marriage is not the legalities or the wedding day, but rather the "commitment to stay together, to be faithful, and to provide the kind of atmosphere that will give growing children stability".

He added: "All the surveys show that children whose parents are married tend to do better, be healthier, and involve themselves less in drugs or crime.

"Listening to the stories of the boys locked up in our Young Offender Institutions about their lack of family support makes me want to weep - and then get very angry that we don't warn people more about the cruelty of having children without a loving father and mother permanently committed to bring them up together."

Bishop Gledhill said that tax breaks for married couples were not the entire solution, and could even lead people to marry for the wrong reason, but were nonetheless a "way of showing that society knows that it depends on good marriages - which it does".