Other people here have reviewed the social comment raison d'etre of this film, and I'll confine myself to the more cinematic aspects of it. It's worth saying, however, re the subject matter that while the particular trade union issue dealt with has now in Britain largely disappeared, and the fifties background nowadays has the air of a period piece, the wider theme of how a dissenting individual with his own point of view and belief is dealt with by a powerful majority is of course of timeless interest.
In cinematic terms the film was always likely to stand or fall on how well the wider social comment and the domestic trials of the strikebreaking Richard Attenborough integrate. In my view they do so pretty well, largely thanks to the presence of Attenborough, a fine character actor, though even he finds it tough to overcome the film's lurches into melodrama.
But there are problems. The direction lacks energy in that the picture maintains a steady pace throughout with no highlights bar the canteen scene where Attenborough flips his lid. There are a couple of visual highlights - a fine crane shot of the final union meeting, and a beautiful, seamless cutaway from Attenborough posed in his son's bedroom to his identically placed presence in the works' canteen. The script, too, struggles to avoid cliche, eg the works manager losing his temper wih the union man who telegraphs his response of: "Are you trying to threaten me?"
Acting is very mixed. Other than Attenborough, Geoffrey Keen as the works manager is as usual excellent, Alfred Burke in the small part of the infiltrated agent provocateur is suitably slimy, but the real problem is Pier Angeli (who incidentally committed suicide 10 years later aged 39) who looks and sounds as if she's walked in from a whole different type of film from Rome via Sunset Boulevard and failed to attend acting classes in either place. Just dreadful!
Well worth seeking out, but don't expect a classic.