What happened is that a father-in-law [call him F] and his daughter-in-law [D] fell in love with one another. Whether D was at the time still married to F’s son, or F was still married to D’s mother-in-law, or both, at the relevant time, is not clear.

Confused? Try pencilling a diagram on a spare bit of paper.

Anyway, by the time F and D fetched up at an English Register Office, neither was still married. However, one or both of their original spouses, F’s son or D’s mother-in-law, was still alive. Had both been deceased, and both F and D been over the age of 21, an exception to the general rule could have been made. Back to the diagram?

So the Registrar, having consulted the Marriage [Prohibited Degrees of Relationship] Act of 1986, and in the light of the fact that the case did not fit the requirements of the exception, refused to perform the ceremony that F and D so dearly wished for, in order to legalise their union.

F and D, determined to contest this decision, took legal advice. The law is exceedingly slow and cumbersome, as anyone who has ever been involved with it will be only too aware. By the time the case eventually went to the European Court of Human Rights in Strasbourg, F and D had been together for 9 years and had a child.

But he or she was not the only child involved. Another had been born to D during her marriage to F’s son. To tease out that child’s legal relationship with the various people involved in this extremely tangled tale would strain the competence of the most expert designer of diagrams. For example, on the marriage between F and D, F – already that child’s grandfather – would also become stepfather.

Article 12 of the Convention on Human Rights, now incorporated into English law, provides the right to marry and to found a family. The European Court listened to the argument that the existing law was designed to protect the integrity of the family. However, they considered that, in real life, there are bound to be situations like this, where fathers-in-law fall in love with their daughters-in-law, and where that love is reciprocated.

In a nutshell, they came to the view that the refusal to marry F and D was a breach of their fundamental human rights under Article 12. And the ruling applies just as much to anyone who fancies marrying his mother-in-law. Does this mean that comedians will have to abandon the mother-in-law jokes?

Maureen Mullally studied law at King’s College, London. She was called to the English Bar at Gray’s Inn and to the Irish Bar at King’s Inns in Dublin. She has practised as a barrister specialising in family law for more than 25 years and now works as a writer and mediator in family disputes.