Dual National leaving UK - Which Passport?

I know I enter the US on my American passport, but when I check in at the airport in the UK for my US bound flight, do I show my EU passport or US passport at that time?  Or does it matter?

Is there any other passport control after you check in and go through security at Gatwick? 

I wasn't sure if I use my EU passport at check in and then arrive in the US with an American passport if that would cause a red flag or something on the US side?

I haven't left the EU since I became a citizen so unsure how it works flying outside the EU.  Thanks.

This is assuming I ever get out of Gatwick which has canceled 2 of my flights already.   

You need to check in with your US passport.  Otherwise you may have problems because your API information won't match.

The airline normally checks your passport when you board, but that isn't border control.

Hope your flight manages to go!

Thanks, that's what I was thinking.  Appreciate the reply. 

I was always told to leave and enter the UK with the UK passport and enter and leave the US on the US one.
So what I do is when leaving UK i check in with my UK passport
When entering US i use US passport
When leaving US i use US passport to check in.
and when returning to UK i use UK passport
SOoooooo thats what i've been doing for years. If its wrong then I've been doing it wrong all these years.

I only ever use my UK passport - leaving and/or entering the US, the UK or any other country. Like Kaylesh, if that's wrong then I've been doing it wrong all along.

(ETA: I'm a naturalised US citizen, so my UK passport came first. I don't know if that makes a difference. Either way, I'll continue to do what I'm doing.)

Found this link on government website..

http://travel.state.gov/travel/cis_pa_tw/cis/cis_1753.html

Thanks.  I'm EU but not UK, so I've already left my home country.  Seems like checking in as US then would make the most sense.  

That way I'll be on the passenger list as American upon my arrival in the US which should cause less headaches on the Advanced Passenger Info thing.

Best bet is what MrsRichUK & Alistair have described, to avoid any difficulties with the US Dept of Homeland Security upon entry to the USA - which I'm all for smooth traveling!  

I'm dual American & British.  When flying to the USA, I:

1) Check in at UK airport using US passport
2) Enter US using US passport
3) Check in at US airport using US passport
4) Enter UK using UK passport

It's not just the question of dual nationality & what you can/can't do - it's to do with the Advanced Passenger Information (API) system where flying into the US, the passport that you use to enter US immigration should match the one on the airline passenger records manifest.  Otherwise, you could potentially run into problems with Homeland Security.  I suppose the UK could end up requiring that too if it wants to be more awkward about things (making this problematic for us duals) but AFAIK the US is far more sticky about it at the mo' than the UK is.

That way I'll be on the passenger list as American upon my arrival in the US which should cause less headaches on the Advanced Passenger Info thing.

Yes!  Cross-posted.  (Traveling to/from the US, I always carry both passports, should I ever be in the situation that I have to produce either one.)

Also if you're not an American citizen (showing your US passport upon entry to the US), Homeland Security will be looking for your visa to enter the country, or that you have pre-registered online for the Visa Waiver Program & any required Visa Waiver form if you're from one of those countries.

My daughter is a Dual National and when travelling we always carry both passports and always use the manned check in desk rather than the self-check because of this very reason. We just hand both of them to the check in person and let them decide which one they need. Also when we went through a passport control just after passing through security in LHR Terminal 1 this past November we handed over just her US passport and the UKBA staff member asked where her visa was, I replied that she was a British Citizen and didn't need a visa and they requested to see her UK Passport.

So My 2p...Carry both. Present both to Check in & Security staff and then when you arrive in the US present your US & UK passport to the Immigration Officer and when arriving in the UK or in Europe present your UK passport to Immigration officials.

I only ever use my UK passport - leaving and/or entering the US, the UK or any other country.

I was previously told by the so-called 'experts' on UKY that if you are a US passport holder, even if you hold a dual nationality, you MUST use your US passport to enter the US.  I think they said there was a potential fine if you don't.     

I was previously told by the so-called 'experts' on UKY that if you are a US passport holder, even if you hold a dual nationality, you MUST use your US passport to enter the US.  I think they said there was a potential fine if you don't.     

I've not heard about a fine, but the other part you are correct:
http://www.usembassy.org.uk/cons_new/acs/passports/dualcit.html

Dual Nationality
In the 1980's, the Supreme Court ruled that U.S. citizenship is a constitutional right that cannot be taken away from a citizen who does not intend to relinquish it. Therefore, such actions as naturalization in a foreign country, travel on a foreign passport, employment with a foreign government, and voting in a foreign election do not automatically jeopardize American citizenship. However, please note that all U.S. citizens, even dual nationals, must enter and depart the United States on U.S. passports.
 

I was previously told by the so-called 'experts' on UKY that if you are a US passport holder, even if you hold a dual nationality, you MUST use your US passport to enter the US.  I think they said there was a potential fine if you don't.      

I've not heard of a fine, but doesn't mean there isn't one.  Some of the Homeland Security immigration officers think they are real bad asses on a power trip though, so I wouldn't be giving them any excuse to have a go at me.  They weren't very friendly or welcoming to DH one time (when we traveled back to my mom's funeral) - nothing untoward, just harsh & unfriendly - and he was traveling with me!  Plus the guy seemed all suspicious of me, as in 'why on earth would an American citizen not be living in the US?!'.  So yep - I'm all for smooth traveling as much as possible.

My daughter is a Dual National and when travelling we always carry both passports and always use the manned check in desk rather than the self-check because of this very reason. We just hand both of them to the check in person and let them decide which one they need.

Honestly, I don't trust airline staff to make the right decision.

Honestly, I don't trust airline staff to make the right decision.

As long as you carry both passports and present them both to each person who asks to see your passport, it really isn't an issue. We travel quite often and have had no issues what so ever.

I'll update how it turns out if we ever get to leave.  Next flight delayed another hour, but at least not canceled yet.