I am a dual US and UK citizen. I was born in the US, but my father is British and I have lived in the UK the last 4 years. I have a trip booked to Spain that leaves tomorrow and through a complicated string of events, my UK passport is lost in the mail somewhere and I will not get it in time for my flight. I do not have a UK driving permit or any other form of proof of identity. I still have my US passport, but it has never been stamped/traveled on in Europe. I've contacted the US and Spanish embassies about my question, but have had no response. I am hesitant to call the airline because I think they would stop me from boarding.
The problem is as follows: because my US passport has not been stamped, there is no record of me arriving in the UK/Europe at all. I am worried they will (a) not let me board my flight from Edinburgh-Seville; (b) detain me or worse deport me (to the US) from Seville; (c) not let me back in the UK at the end of the trip.
Has anyone been in a similar situation? What should I do? Can I still go on my trip or is it a bad idea? What evidence can I provide to support my claims?