Sometimes we hear stories where passengers who accompany a child are questioned when the relationship between the child and the passenger is not immediately clear. The questions seem intrusive and appear to be unreasonable, and in some cases an IO may insist upon seeing supporting documents that establish the relationship between the passenger and the child.
As an example from a personal standpoint, my wife retains her maiden name on her UK passport, but she may travel with my son who uses my family name. This is a situation where the relationship is not immediately clear. What can they expect when they travel to a UK (or EEA) destination? Should they bring my son's birth certificate as a supporting document?
This question has established that the term 'birth certificate' is absent from any relevant legislation. And yet the question describes an incident where an IO wanted to inspect a birth certificate. Was the IO acting unlawfully? Could a different document be substituted and accomplish the same purpose?
Also the referenced question is about UK citizens arriving in the UK. If the traveller and child are Canadian does it make any difference?
Question: Is there a legal foundation for the IO's behaviour? If so, what is it and what should passengers be aware of?
NOTE: the referenced question asked a highly specific question about whether or not an individual is required to present a birth certificate in certain occasions. This question seeks to know if the IO's line of enquiry is lawful and if so, how arriving passengers can best prepare themselves. What if you don't have a birth certificate to hand?
My personal circumstances are best met by answers directly relevant to travellers arriving in the UK. But authoritative information on EEA members are also highly relevant.