I am a British man living in Spain married to a Spanish woman, our son has both British and Spanish nationality.

I plan to go the UK alone with him for a week and wanted to ask about if I'm likely to have problems leaving Spain or entering the UK with border agents as my wife won't be travelling with us. In cases where the parents are divorced (we remain married) I've heard stories of the border agents in both the departure and arrivals countries suspecting that the father may be taking his child on a one way trip without intention to return. (Note I have a return flight booked and can demonstrate this with the reservation if asked).

Is this likely to be an issue? Is there anything I should do in advance to prepare for this eventuality?