Most people born in Northern Ireland have or are entitled to dual citizenship, British and Irish. Generally people apply for the passport of the country which they identify with — nationalists for Irish passports, unionists for British — and are never troubled by the legal fact that they may technically possess the other nationality as well.

The recently reported case of De Souza (Good Friday Agreement: nationality) United States of America [2019] UKUT 355 (IAC) is part of a campaign, led by the redoubtable Emma DeSouza, challenging this state of affairs. Ms DeSouza accepts only her Irish citizenship and strongly objects to having British nationality, to the point that she will not use the procedure available to renounce it (as that would be to acknowledge having British citizenship in the first place).

Ms DeSouza says that her position — that Northern Irish people cannot be forced to start life with dual citizenship — is supported by the Good Friday Agreement. That is because the UK and Ireland said in that agreement that both countries:

recognise the birthright of all the people of Northern Ireland to identify themselves and be accepted as Irish or British, or both, as they may so choose, and accordingly confirm that their right to hold both British and Irish citizenship is accepted by both Governments and would not be affected by any future change in the status of Northern Ireland.

This campaign has gained the support, or at any rate the attention, of the prime ministers of both countries. The attempt to change the legal position on citizenship via the courts has, however, been rejected by the Upper Tribunal.

The case arose out of Mr DeSouza’s visa problems, as an American who wished to live with his wife in Northern Ireland. In an attempt to avoid being caught by the notoriously harsh family immigration rules that apply to the spouses of British citizens, he applied for a residence card as the spouse of an EU citizen.

The Home Office said that this procedure is not available to people who have British citizenship, Ms DeSouza being legally a UK citizen as well as Irish. This will be little surprise to lawyers familiar with the case of C-434/09 McCarthy, in which the facts were similar.

The First-tier Tribunal found that “the constitutional changes effected by the Good Friday Agreement with its annexed British-Irish Agreement, the latter amounting to an international treaty between sovereign governments, supersede the British Nationality Act 1981 in so far as the people of Northern Ireland are concerned”.

The Upper Tribunal reversed this finding. The headnote to its decision says simply:

The Belfast (or Good Friday) Agreement did not amend the law of British citizenship, as contained in the British Nationality Act 1981.

That is a very short official summary for an Upper Tribunal case. It reflects the fact that this is Law 101: international treaties do not override Acts of Parliament (or indeed Acts of the Oireachtas in Ireland).

Members of the public are, of course, entitled to be surprised that a treaty as eminent as the Good Friday Agreement doesn’t have that effect. But the Upper Tribunal pointed out that it is not altogether clear that the “birthright provisions” quoted above were ever intended to give someone the right to reject his or her Irish or British citizenship, in a legal rather than personal identity sense. If the point was to give people the right to turn dual nationality on and off at will, it is “inconceivable” that the Agreement wouldn’t have said so explicitly, or that this would not have been written into the Northern Ireland Act 1998.

The judgment also raises the possibility that citizenship by consent was never intended or devised because it would be unworkable. It said that “a person’s nationality cannot depend in law on an undisclosed state of mind, which could change from time to time, depending on how he or she felt”.

There is also the minor snag that it would mean everyone in Northern Ireland being born stateless: if the UK could not confer automatic citizenship at birth to Northern Irish people, nor logically could Ireland. Such a result would be in breach of the UN conventions on statelessness, which both countries have signed.

The Upper Tribunal, understandably, was in no rush to violate one treaty in the name of another. The couple are crowdfunding in the amount of £120,000 to take the case to the Court of Appeal — but if there is a satisfactory solution, it seems more likely to emerge from politics rather than the law.