And you've met every communist party member and every communist agent/saboteur who lived through that period?
If you caste your mind back NONE of the communist agents who were exposed in the popular Press looked like anything but very ordinary people. That's what was so disturbing for many people - the fact that you could be a friend, work colleague or acquaintance for someone for years without realising that they were an agent of a foreign power.
You might also remember that this was a period when strikes were comparatively frequent and on numerous cases one or more of the union leaders was found to be a communist. Were such people "acting on instructions from Moscow" as the Press frequently suggested? Who knows. It certainly felt like the country was under a constant threat which quite quickly developed into the full-blown "Cold War" and the seemingly imminment threat of nuclear destruction.
I'm guessing, since the Boulting Brothers were reasonably intelligent people, that they knew precisely how realistic/unrealistic their production was - and that this mattered very little in terms of it's purpose - to allay people's fears, to a certain extent.
Unless you believe that the Boultings knew you and your family when they made the film, and deliberately tried to blacken your reputations, is it possible that you have taken the film rather more personally than was ever intended?