The last time I went from France to the UK by tunnel, I had a bit of an interesting experience I thought I would share:
The whole family was in the car and we were right at the point where you show your passport to the UK border officers. Our line was taking forever, other cars were backing up and going to other lines that were free. We had passed through the hatched area with the big yellow scanners and were the next car in the queue. We saw that the signal light above had changed from green to a red X and cars behind us were directed to back up and change lanes.
I noticed that there was a very wide gap in the bollards and that I could easily drive through it to switch into the next lane. Nothing crazy or dangerous, there were no other cars around, but plainly not exactly following the directions. So I did it and moved into the next lane. Immediately, the Border Officer came out of his booth and started yelling at me. Another Border Officer told him that the lane I was in was closed at the same time I was explaining it, but he still gave me a lecture about "the bollards are there for a reason". I know you are never going to win an argument with those guys, so I say sorry and shut up. But the Border Officer is now angry.
We get to the window and hand over the passports. I have two passports, an expired one with my visa in it and my current one. I always hand over both and explain, they understand immediately and it's never a problem. This time, the guy starts asking a bunch of questions about where I work and do I have a limited company and so on. After a few questions, he gives us back the stack of passports and we drive on.
As she is putting everything away, my wife notices that my old passport with the visa is not there! That dodgy guy had taken it. We stop and she runs back, he gives it back with a mumbled "sorry" and we continued on.
I'm convinced that this guy was mad at me and figure out that my old expired passport was the only visa I've got. Without that, I can't enter and leave the UK, could have trouble working and renting a place. He know that loosing that would screw me over in a huuge way, and would take me months of grief to fix. So he took it. Dickhead.
Weird, because those guys are normally pleasant. I'm not doing anything wrong and they usually treat me accordingly.