A Christian charity has denounced a Supreme Court ruling in favour of extending civil partnerships to heterosexual couples as a 'fundamental attack on marriage'.

Rebecca Steinfeld and Charles Keidan had argued that it was incompatible with their human rights to deny them the same opportunity to enter into an opposite-sex civil partnership as a same-sex couple. They said the 'legacy of marriage' which 'treated women as property for centuries' was not acceptable to them and that civil partnership was a 'modern, symetrical institution'.

Their barrister Karon Monaghan QC told the court they had 'deep-rooted and genuine ideological objections to marriage'.

Civil partnerships have been available to same-sex couples since 2004 and offer the same legal and financial protection to couples as marriage. The decision to legalise same-sex marriage in 2014 means that gay couples have the option of either, whereas opposite-sex couples do not.

The ruling overturns a previous judgment against the couple by the Court of Appeal last year, but does not automatically mean that the law will change.

However, Ciarán Kelly, deputy director of The Christian Institute, told Christian Today the decision was 'unnecessary and unhelpful' and called instead for a 'fundamental review' of the law about civil partnerships. 

In a Christian Institute release he said: 'This is yet another fundamental attack on marriage from a court system that seems determined to do all it can to undermine it.

'The couple who brought this case objected to what they called the "sexist trappings" of marriage. But that is to fundamentally misrepresent what marriage is about. Marriage – with its public promises of life long faithfulness – is the gold standard of commitment. It is beneficial for the individuals involved and for society as a whole.

'With this ruling the court has given its backing to "marriage lite" – all the benefits of marriage but without the responsibilities.'