A leading UK family lawyer has said the law in England and Wales no longer has a clear concept of marriage.

Baroness Deech, the chairman of the Bar Standards Board, in a public lecture yesterday, said that some differences between civil partnerships and marriage should be preserved, and criticises recent Labour laws that allow lesbian couples to be named on birth certificates with no mention of a father.

She added that she believed that same sex parents are bad for children if they deprive them of the influence of a father or mother.

The crossbench peer made her comments in the latest of a series of public lectures as professor of law at Gresham College, London.

Baroness Deech, who is also a former chief of the Human Fertilisation and Embryology Authority, also condemned laws which allow same sex parents to put both their own names on a child’s birth certificate.

She has previously considered the idea that families could be forced to look after grandparents in their old age, and claimed that only “the gold digger” would benefit from rules giving cohabiting couples the same rights as spouses.

In her address, Lady Deech asked whether the logical conclusion to the liberalisation of society was that same-sex couples should be allowed to marry, given that the differences between civil partnerships and traditional weddings have been “eroded”.

At the same time, attitudes to adultery, divorce and single mothers have been relaxed while fewer people are getting married and tax breaks for wedded couples have been removed.

Lady Deech quoted a famous legal definition of marriage as the “voluntary union for life of one man and one woman, to the exclusion of all others.”

She said: “Such is the transformation of family law and family life that not one word of this remains true.”

Lady Deech pointed out that the number of weddings has fallen to its lowest level since 1895 because “religion is a waning force, women have financial independence, there is state support for lone parents, children are no longer classified as illegitimate, divorce is easy and there is no recrimination over sex and birth out of wedlock”.

She conceded that two attempts to use the Human Rights Act to claim that same-sex couples should be allowed to marry have failed.

But she continued: “In the passage of the few years since this judgment, it is possible that societal views have shifted sufficiently so that an appeal on the same grounds might have a different outcome.

“Whatever might be held, one still concludes that English law has lost any clear concept of marriage.”

She concluded that “civil partnerships do still differ from marriage a little, and this is an area where the difference ought to be preserved with justification”.

This was because she disagreed with provisions of the Human Fertilisation and Embryology Act 2008, which allow same-sex couples to be named as parents on birth certificates with no reference to a father.

“This is not a moral issue; it is about disguising true facts, and it is about confusing biological parenthood, legal and social parenthood.”

She also criticised Labour’s decision to remove the need for doctors to bear in mind a child’s “need for a father” when considering fertility treatment for a woman.

“I regret the downgrading of the father as a person of importance – the legislative dismissal of the contribution of half the population to the upbringing of the next generation.”

She concluded: “The limit to same-sex relationships is that they cannot be a reproductive unit in a way that is best for the welfare of the child if they cut out all contact with members of the other sex or falsify the birth registration. Tolerance of both types of parenting has to be ensured.

“There is a wealth of research showing that children need fathers, not just two parents. Children need to see complementary roles, the relationship between the sexes, a microcosm of society, as they grow up.’

Britain was at the bottom of international league tables for child welfare, Lady Deech said, adding that boys do worse without father and girls benefit as well as boys from their presence.