Originally Posted by mozilla

Yes and no. The airline files the APIS information with the authority. But some airlines allow passengers to fill in the supplemental data themselves that is required for APIS, often at the time of reservation or as soon as the reservation is ticketed, and up until check in. OLCI may require it before proceeding.

I've received boarding passes for flights to the UK (on BA), and the EU (for destinations that require APIS), and the only time my passport was checked was a cursory check with boarding pass at the gate. I was about to say I had similar experiences traveling to the US, but the airline's app did scan my passport or had it on file.

Note: not every airline allows this, and it may not be allowed for every destination.



Not in the way you experience it in the EU, but similarly to the US, carriers (airlines, boats, Eurostar, Shuttle, etc) need to report to British immigration who is leaving. So an exit record is kept.



It's possible your Spanish passport has been flagged in the UK database for the exit with no matching entry - although the border agency could've stopped you at the gate if they really wanted to investigate - and if you attempted to enter using that passport you may be referred to secondary. APIS wouldn't be denied as there is no proof of actual illegal immigration, it would be up to the border agent to find out what happened.

An APIS entry that can't be matched with an actual presentation is not a concern. The passenger that the APIS record refers to would not be considered immigrated or illegally immigrated.