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
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.