It's hard to tell from the musty tomes which keep track of Law Lords' rulings whether Baroness Hale of Richmond deployed the intonation of John McEnroe - "You cannot be serious!" - or of Victor Meldrew - "I don't believe it!" - when she came to pronounce on Articles 14 and 15 of the Adoption (NI) Order 1987 as amended by the Civil Partnership Act of 2005.

At any rate, she reckoned she'd never heard anything like it.

The baroness was one of a panel of five law lords in 2008 dealing with the "P" case, involving a Northern Ireland couple who had been rejected as adoptive parents because they were unmarried. The woman was the mother of the child. Although the man was not the biological father, the couple had been living together for some time and related to each other and to the child as a family. The couple had challenged the validity of the law on the basis that it deprived them of their rights under European equality legislation.

Having looked at the law on adoption as it stood, the panel concluded, in Baroness Hale's words: "This must have been a mistake." But now it turns out that it might have been the baroness who was mistaken. It could be that the legal position which their lordships found incredible was what legislators in the North had intended.

The difficulty lay in the fact that Article 15 of the NI Adoption Order as amended by the Civil Partnership Act gave people who were neither married nor in civil partnerships the right to adopt, but only as single persons: they couldn't adopt jointly. Article 14, which wasn't amended by the Civil Partnership Act, gave married people only the right to adopt jointly.

So the law on the face of it meant that people in civil partnerships, because they didn't fit into either of the specified categories, couldn't adopt either singly or jointly. A gay person in a civil partnership was thus disadvantaged in relation to adoption compared to a gay person not in a partnership.

It seemed to Baroness Hale and her colleagues that this was such an obviously anomalous situation that it cannot have been intended. Other considerations apart, she said, "It is difficult to see how this could survive a challenge under article 14 of the European Convention, which takes a particularly firm line against discrimination on the ground of sexual orientation."

What is now emerging is the possibility that the supposed anomaly was allowed to stand expressly to perpetuate discrimination on grounds of sexual orientation.

On December 12 last, the High Court began hearing a complaint from the NI Human Rights Commission that the Department of Health, by failing to deal with the anomaly unearthed in the P case, was in breach of a duty to bring adoption procedures into line with human rights law. The case was adjourned on its second day after Attorney General John Larkin, acting for the Department, launched a legal exocet against the commission.

There was no anomaly to resolve, Mr Larkin argued: the ban on civil partners adopting which arose from the two Articles hadn't come about through misunderstanding or inadvertence but had been engineered so as to reflect the wishes of the legislators, which it was not the court's business to overrule.

The legislators had been concerned to prevent law and practice on adoption being changed "by the back door".

Or to put it another way, no adoption by gay couples until Stormont says so.

Granting an application from the commission for an adjournment to consider the implications of the submission, Mr Justice Treacy wondered how, if the situation identified by Baroness Hale as a glaring anomaly was now being said not to be an anomaly at all, but in fact to have been intended all along, how can it have been that nobody had pointed this out to their Lordships at the time of the P case?

"How on earth a massive mistake like that could have been communicated to the House of Lords and nobody saw fit to (correct it), I have great difficulty in understanding."

We may hear more on this matter when the High Court hearing resumes in March.

The Belfast writer Catherine Couvert, who has followed this issue more closely that anyone else as it has coiled through the labyrinthine ways of Northern law and civic morality, has observed: "Whether the change comes through courageous politicians...or through a judicial review, it is going to come anyway."