I had a stop and flight change at Heathrow in November- switching from one airline to another coming from Amsterdam and going to Philadelphia. For anyone who doesn't know Heathrow it's a security stringent airport. I asked about hand checking my film, and the person was kind enough to take my film to show to and ask his supervisor about a hand check. In the end, since it was only 400 speed film, he sent it thru the machine- BUT it would have taken FAR less time and energy to just hand check the film rather than chase down the crew boss, ask, and run back saying no. I was flying in on Vueling out of A-dam and flying out on British Airways, you cannot make a connection at Heathrow without going thru passport control, security etc, both inbound and out again. I always check a bag where I put my tripod and things I cannot carry on, then have a carry-on bag such as my usual medium size messenger bag, that fits under the seat, for carrying cameras, film, some reading material for the flight, water & snacks, phone charging battery, cords etc, and maybe my iPad.