Donald Macintyre's Sketch: The case against? It's all about dynasties, of course

Labour's Lord Faulkner had just admiringly described the euphoric scenes in the New Zealand parliament which followed the passage of its own gay marriage bill – culminating in the lusty singing of a Maori love song – when Lord Vinson rose to his feet. To describe the Tory peer as unimpressed would be a serious understatement.

Declaring that the (British) Bill would make "sexless" the terms "husbands and wives", and claiming that in Spain parents were already known clinically as "Progenitor A and Progenitor B", Lord Vinson went on to deploy a genuinely novel argument.

Heterosexual marriage did something that by "its very nature homosexual marriage cannot do". This was the "consanguinity", underpinned and linked by procreation, which joined "two families, two tribes, two dynasties linked by their bloodline thereafter for mutual support and protection". Never mind that gay couples have been known to have children, and it was not immediately clear why they should not have in-laws too. The image he conjured was seductively medieval, from an era when marriage was conducted to end wars and expand territory, kingdoms even.

Two arguments raged simultaneously among the peers. One was over the merits of the Bill itself, which at times transformed the Upper House into a kind of new-age encounter group in which (especially the heterosexual) supporters of the Bill were irresistibly drawn to describe the experiences of gay people they had known well.

Lord Birt, of BBC fame, described the development from the sixties of the late Kenny Everett, with whom he had worked and who had progressed from admitting that as a teenager he had experienced "unfathomable stirrings in the presence of handsome young men" to gradually embracing his "true nature". And the Liberal Democrat peer Lord Carlile eloquently described the richly fulfilled and stable same-sex relationship of one of his own daughters, asking opponents: "If any of your married lordships would feel any less married if Anna and Joanna were permitted lawful wedlock?"

But the other was over the constitutional propriety of Lord Dear's amendment (vainly) seeking to block a second reading of a Bill already approved by the Commons. Lord Cope was fairly withering on this point. The question, he said, was "whether the Commons or we are the better judges of changing attitudes on matters such as this. I do not think with our average age we are the better judges." Cope was on the winning side last night. Given the approach at least of Lord Vinson (82) he probably had a point.