The full meaning of durable relationships would be interpreted by the courts in “hard cases”, using a wide range of measures including whether others send the partners a Christmas card, the chair of the Electoral Commission has said.

There is ongoing debate about whether polygamous and polyamorous relationships would be covered in the proposed expanded concept of the family, among other relationships, in the upcoming referendum.

Ms Justice Marie Baker said terminology introduced into the Constitution had to be “specific but not too specific,” to allow for examples “that haven’t yet been considered”.

She added that interpretation of what was a durable relationship would be somewhat subjective.

“There are all kinds of things, some of them are subjective and some of them are objective. So subjectively, a relationship is durable, if committed, if it presents itself as committed, if it means to be committed, if it intends to be committed.

“Its durability can sometimes be how you are treated by other people. Are you are you invited as a couple to weddings? Do people send Christmas cards to both of you? These are the indicators of your commitment to each other,” she added.