Given that the Government's plans to legalise gay marriage have been strongly and very publicly opposed by leading members of the Church of England – including a former Archbishop of Canterbury and the current Archbishop of York – it would have been unrealistic to expect anything like a welcome from the generally more conservative hierarchy of the Roman Catholic Church. Even so, the ferocity of the language used in a newspaper article yesterday by Cardinal Keith O'Brien, leader of the church in Scotland and the most senior Roman Catholic cleric in Britain, almost takes the breath away.

In his article, for The Sunday Telegraph, Cardinal O'Brien described the concept of gay marriage as "a grotesque subversion of a universally accepted human right" and its recognition in Britain as a development that would "shame the United Kingdom in the eyes of the world". He went on to argue that "same-sex marriage would... create a society which deliberately chooses to deprive a child of either a mother or a father". Quite how he reaches this particular conclusion – single-parent families hardly being a rarity these days and homosexuals, singly and in couples, making successful and fulfilled parents – leaves a host of questions.

The substance, but even more the tone, of his condemnation, however, suggests a church leader who is remote from the society in which he lives and lays claim to philosophical and judicial territory that is not his. There will be clerics who reject single-sex marriage on doctrinal grounds – grounds which can themselves be open to different interpretations – but it sits ill with the mantle of leadership for the country's senior Roman Catholic leader to characterise the policy of an elected Government as "madness" (the cardinal's word). As the Equalities Minister, Lynne Featherstone, said recently – and rightly – in defence of Government policy, "not even the Church" owns marriage.

With attitudes towards homosexuality becoming more tolerant, even – according to a just-published book – among that cruellest of groups, schoolchildren, society is changing. Civil partnerships represented an enormous advance. But the legalisation of gay marriage would remove one of the last obstacles to full homosexual equality before the law and stand as a testament to more enlightened times.