The Home Office has released its seasonal advice for parents travelling with children whose surnames they don’t share: take supporting documents to avoid being cross-examined at customs. Well, not exactly – it’s closer to: “Expect to be cross-examined – then make sure you have supporting documentation if your child fails the cross-examination.”

Birth or adoption certificates are preferable, but other recognised proofs are divorce and death certificates, or a letter from the parent with the right surname, or if you prefer, the proper parent.

This is meant to tackle child-trafficking, but it is highly debatable how many real-life instances would be picked up. Europol has identified two main methods – one, to travel on documents forged in Nigeria or China (a passport is harder to forge than a death certificate, and would probably be forged in a matching surname to begin with); two, to arrive without documents, then abscond from border control to the trafficker.

To catch a criminal, this net is probably too much hole and not enough string. It is perfect, on the other hand, for the catching of divorcees, married women who declined to take their husband’s name, LGBT couples, any family that deviated from the hetero-nuclear norm.

Anecdotally, parents have reported border controls replicating everyday prejudices in a high-stakes environment; women of colour saying they are more likely to be stopped when they are not with their white partner, even if he doesn’t share the child’s surname, either. In my family of five, we have three surnames (my husband and his daughter’s; mine, only shared by the dog who doesn’t have a passport; my two children, who have their father’s name), and I can say with relative confidence that we only get stopped when we have somehow annoyed the official. Then they interrogate the eight-year-old, our youngest, and we all stand frozen to the spot in case she decides it would be hilarious to pretend she has never met us. This makes us look extremely shifty.

The punitive edge is not in the check itself – everyone wants child-trafficking victims protected to the nth degree, even by a measure unlikely to work – but in the fact that nobody has thought creatively about how to remove the wrongly named but otherwise perfectly legitimate parent outside the pool of the suspect. It would be perfectly possible to name your children in your passport, or link the documents electronically. But authorities simply don’t care to; the unconventional might not need the extra scrutiny, but by some tacit 50s code, deserve it.