UK Government should focus on the social definition of marriage rather than the religious, argues Miles Geffin

What exactly is marriage? According to the 1969 Revised Canons Ecclesiastical, the Church of England's definition of marriage is: "A union permanent and life-long; for better for worse; till death them do part; of one man and one woman; to the exclusion of all others on either side; for the procreation and nurture of children; for the hallowing and right direction of the natural instincts and affections; and for the mutual society, help and comfort which the one ought to have of the other, both in prosperity and adversity."

But whether conducted at a civil or religious ceremony, marriage is a social contract rather than a religious one. That contract is regulated by the state, not by religious organisations. 

Under current UK law, the essence of the contract has been described by Sir James Munby, the new president of the Family Division of the High Court, as: "An agreement between a man and a woman to live together, and to love one another as husband and wife, to the exclusion of all others. The marriage contract creates a relationship of mutual and reciprocal obligations, typically involving the sharing of a common home and a common domestic life, and the right to enjoy the other's society, comfort and assistance."

In many respects, the legal and religious definitions are similar, but the differences are important. The social contract involves no obligation on the participants of marriage to procreate.

The social contract, unlike the religious one, also anticipates that a marriage can end other than by the death of one of the spouses. Indeed, if a marriage breaks down, the State – through its courts – may be enjoined on the application of one or other of the spouses to make orders in relation to parenting and financial issues. Likewise, love – implicit in the Church of England's definition – is explicit in the social contract. 

These differences tend to inform the debate surrounding same-sex marriage, but it has ever been thus.

In 1957 the authors of the Wolfenden Report, including my firm's founder Lord Mishcon among their number, concluded that: "Unless a deliberate attempt is to be made by society, acting through the agency of the law, to equate the sphere of crime with that of sin, there must remain a realm of private morality and immorality which is, in brief, not the law's business." 

The Wolfenden Committee's recommendation that homosexual behaviour between consenting adults in private should no longer be a criminal offence led, a decade later, to the introduction of the Sexual Offences Act 1967.

Fifty-six years later, the deployment of the word "sin" by the Wolfenden Committee may jar.  

But even 25 years ago, Section 28 of the Local Government Act 1988 was introduced, prohibiting local authorities from intentionally promoting homosexuality in maintained schools and describing committed same-sex partnerships as "pretended family relationships". It was only as recently as 2003 that Section 28 was repealed.

Today, the Coalition for Marriage argues that marriage reflects the complementary natures of men and women. Any redefinition of marriage to include same-sex participants would, the Coalition argues, mean that "people's careers could be harmed, couples seeking to adopt or foster could be excluded, and schools would inevitably have to teach the new definition to children". 

Unburdened by such considerations, the proponents of same-sex marriage have perhaps the easier argument. 

Barack Obama chose his second inauguration speech to promote same-sex marriage. Channelling the spirit of Thomas Jefferson, he argued: "If we are truly created equal, then surely the love we commit to one another must be equal as well".

The publication of the long-trailed Marriage (Same Sex Couples) Bill, was similarly heralded by the UK Government as necessary to ensure same-sex couples were treated "equally and fairly". It is predictable that ministers will, in the foreseeable future, legislate to alter the social contract of marriage so as to include same-sex couples. The necessary amendment is fairly modest as was demonstrated by the legislature of Canada which introduced same-sex marriage in 2004. Under Canadian Law, marriage is now "the lawful union of two persons to the exclusion of all others". 

It was the application of this interpretation of marriage that led the Superior Court of Ontario to declare earlier this year that a UK civil partnership was a marriage under Canadian Law. Indeed, the Ontario Court held that the current distinction in UK law between civil partnerships and marriage "violates human dignity".  

Once it is accepted that marriage is a social contract, not a religious one, it is hard to argue otherwise.

Miles Geffin is a legal director in Mishcon de Reya's family department. He was instructed as an expert witness for the applicant in Hincks v Gallardo [2001] ONSC 129 [7 January 2013] – Superior Court of Ontario.