I know I still have to show my passport when I go to the UK.
That is because the man at the desk likes to look at
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passports!
At airports yeah definitely. Not sure about euro tunnel. There are ways she could get into France, through The Basque at certain times of day. I am not sure what French authorities would do. She is a British Citizen. Would they return her to Spain?
Lurch has the means to get people in UK, he drives a big scania and crosses the border often. But he would not smuggle his own daughter into UK.
There are a few things we could do, but best to do this properly.