Legal right to hold a passport

[guest]

Not sure if I am posting in the right place, but I would appreciate any advice.

A woman I know split from her DH, remarried, and left her kids with their father to move abroad with the new man.

The children's father has since brought them up. The woman left one of her children's passports with a relative of the new DH. She has instructed this relative not to pass the passport onto her ex. The exDH is concerned that the woman might be planning to take one of the children out of the country, effectively abducting the child.

Does anyone know whether it is legal for someone other than a child's parent to refuse to hand over their passport. What action should the exDH take to ensure that his child is not taken from this country without his permission? Or can the child's mother take her child abroad without his permission (even though the child has been living with him)?

Is there a way of getting rteplacement passports on the grounds that the partner with residency has 'lost'them? I would ring the Passport office and ask for advice.

The parent can't refuse to hand over a passport either. A friend as resident parent, had been court ordered recently to hand her dc's passports to her xH solicitor.

Thanks for your input. Will give info to friend.