I will be flying from Amsterdam to London Heathrow airport. There I will board my second flight from Heathrow to Los Angeles. These two flights are not connecting, just hours apart. My question is will I have to go through customs twice? When I arrive and when I prepare to leave again? Or can I just travel from terminal to terminal? I’m aware I will have to check in for my last flight, but I’m. It sure if I have to leave and go through security again.