I just got back from a trip to Scotland, and passed through security in Toronto, Heathrow and Edinburgh.
I had a Pentax 67, 4 lenses, and about 25 rolls of 220 film in a Lowepro backpack.
I ran the whole thing through the scanners. Nobody blinked in the UK, just passed it through. The guy in Toronto insisted on opening the case, and pawed through my equipment, picking up lenses by the lens caps (!!!) - I was waiting for one to drop
.
Fairly consistent - the only place I have been hassled, on a few occasions, is Toronto. This includes most major West European and US airports.
BTW, the films were in a clear ziplock bag, only removed from the cardboard boxes.
Hope this helps.
Jaan