Airports do have the capacity to swab individual items for explosives, and it's happened to me on a handful of occasions - always a slight concern as I work with some explosives on occasion. In the days when i used my work bag as a cabin bag, that was a potential issue!
But the swabbing of individual items takes time and costs money to run the test even though it's automated. Simply running every bag on a conveyor through the x-ray machines takes no time and no additional cost. Most people already complain at the time spent queuing up for airport security...can you imagine if explosive swabs were routinely taken of hand baggage? Or were available to everyone on request?
The whole "damaged property" thing is simply irrelevant. You voluntarily submit your film for scanning along with your bag, or you remove it. The airport ought to have a sign warning about photographic film, and I note reports that some are doing this. You have the choice not to subject your film to the scan. You either don't pack it in the first place, or you choose to bin it at the security check. Or you take the gamble. That is the way the law will be interpreted. It's not the same as some security person fumbling your £3000 laptop and dropping it. Or the conveyor belt malfunctioning and ruining your luggage.
And I am totally with foc on attitude towards these people. Being compliant gets you a lot further than even a polite argument. "Making a scene" to me means drama, it means an argument - even if polite. And that's a one way ticket to trouble in an airport. I've never had any issues with any airport security people including LHR. That doesn't mean they haven't questioned me about the seven cameras and baggie full of film, or about the under water camera housing. It means that I am compliant when asked about them. I offer to unpack everything to show them, if that's what is desired. I describe the contents, in a calm voice that is neither angry nor impatient. And I get through without any real hassle, every single time. Whereas the number of people I see who show even slight loss of patience who are taken aside for extra checks, warned they might be denied boarding, given a verbal dressing down by the security staff....is more than I can remember. The staff at LHR are certainly busy and probably over worked. They know their job is important but generally looked upon as an inconvenience by travellers. they will not respond to small talk. It's a case of "speak when spoken to". They are under no obligation to cede to requests for hand inspection of film or any other items. They're working in what, by some metrics, is the world's busiest airport. And part of their job is to get people through quickly. When they do talk, they're generally OK. though I do recall one time when I was asked at LHR if I had electronic items in my hold luggage for a flight to San Francisco, I responded "cameras" and that didn't gel. They called me back a few minutes later and said "You have electronic items in here!"....but it was all sorted in a civilised manner.
I did try to email London Luton Airport yesterday to ask about their scanners, but that seems impossible. Questions about security seem to direct one to the Department for Transport web page and the general enquiries web form requires a flight number and date to be entered. Maybe a more general enquiry with the DfT is necessary.