I scanned into the wrong terminal (apparently at Gatwick at the time it didn’t tell you when you scanned in).. so when I realised 20 mins after going through security and not seeing our flight on the board, I went and asked how I could switch terminals.. they told me I couldn’t do this and had to go through immigration and go to the airline desk and get another boarding card.. I ran to the other terminal and got to the check in and asked the gentleman if I could quickly speak to the desk agent.. He was very kind and let us do this and the agent printed out new boarding passes.. we got to security and I looked at the passports and noticed one wasn’t mine.. handed it to the person I was with and then opened the other one and realised it was his.. the agent had given me the gentlemans passport.. I ran back as fast as my legs could take me and luckily he was still at the desk.
We managed to get to the gate with 15 mins to spare.