I have a US and an EU passport. I live in California, and travel to UK about twice a year.

On previous trips, I used only my US passport. On the last 3 trips, Heathrow immigration asked (seeing in my US passport that I was born in UK) why I do not have a UK passport. So this time I'll take both passports with me, and use the EU passport at Heathrow.

Does it matter which passport I present to the airline (United)? Are there any pitfall to what I doing?

Thanks to all,
John, San Diego