Help! Travelling with two passports - how does this work?

[kraken]

I feel a bit of an idiot asking this, but I'm losing the plot here, and I know there's a fair few dual citizens who'll know the answer to this.

As of last year, I have a UK and an EU passport. The general rule to dual citizenship travel is to leave and enter a country with that passport, which makes perfect sense. You leave (and enter) the UK with your UK passport, you arrive in (and depart) the EU with your EU passport.

Except I'm not sure how this actually works in practice with boarding passes and adding a passport number onto a return booking - surely I can't have a different passport number on the ticket for the different journeys, but I need to present my boarding pass with my passport at the airport, right? 

Or is there a "present passport only" bit at airports? I have to admit I've never paid attention to whether I'm presenting just my passport or the boarding pass as well when I go through different check points at an airport. Am I presenting a different passport at different points?

I have googled, but as all the info I can find focuses on more complexities such as visas and third countries, maybe I am just being thick.

Can someone give me the idiot's step-by-step run through of how this works? I'm flying into the EU, for context.

[scicaro]

I usually register my UK passport for the flight and use this at UK passport control and when Boarding.

When I go through passport control here in Denmark (entering or leaving) I show my Danish passport. They don't ask for the boarding pass.

[scicaro]

When I say "usually" I've only flown to the UK since I got the extra passport.

[kraken]

Thanks scicaro, I'm thinking in my case I probably ought to reverse and use the EU passport with the tickets.

[sprite]

On my last journey, it was Dublin--> Canada, Canada --> UK.
I booked the flight and gave my Canadian passport details, because that is what I would be using to enter the country for the start of my flights. There are no immigration exit passport checks in Ireland or the UK, the passport is solely used to prove your identity for the airlines, so the nationality doesn't matter.

On return, I used my UK passport for everything. Again, there are no immigration checks when leaving Canada.

[sprite]

I didn't give my UK passport to the airline, it didn't seem to make any difference.

[kraken]

Thanks sprite 😊

[lillielangtry]

Yeah, I honestly don't think the airline is really bothered which you put as long as you can show both if necessary. (Possibly they are stricter if you are entering a country you would otherwise need a visa for, I'm not sure)

Last year I got totally muddled trying to check in online with Eurowings and ended up entering one passport number and then the other - can't even remember in the end which was successful!

When I got to the airport in Germany, I accidentally showed the police officer at passport control my British passport. He then wanted to see my residence permit, to which I said, "oh I don't have one, I have a German passport", to which he replied very patiently, "then I need to see that, don't I". Oops.

Pretty sure you'll manage to be more competent about it than I was!

[kraken]

I think I'm just a bit nervous as I haven't done it before. Yeah not worried about airline as they won't care, it was more passport control and not remembering if they want to see a matching boarding pass as well or not.

I can so see myself presenting the wrong passport somewhere, I hope if I do mine pans out the way yours did lillielangtry