The supreme accolade for a 'B' film is that so many cinemas should choose to show it as a main feature, and it gets translated into at least one foreign language - the case with this production.
You can't help noticing how tiny the budget must have been. Just a handful of modest room-sets, no location work, no special effects, no big-name stars (even Derren Nesbitt was probably not bankable as early as this). Yet its smallness is its strength. We are able to focus on an average English town living the second-division life. A group of three gangsters, somewhat out of their depth, try to exploit the quiet holiday period to pull-off their one and only robbery before going straight. According to plan, one of them bluffs his way into a bank, wearing postman's uniform, before letting-in the other two, and they tie up the manager and his secretary who are alone in the building. But they hadn't thought about the office cleaners who would naturally come on duty at a quiet time like this, so the gang has no choice but to lock their two captives in the strongroom that they've just burgled.
Driving off, they realize that the unfortunate couple will soon run out of air, so they have to devise a plan to enable the cops to get hold of the strongroom keys in time to rescue them. Otherwise the robbery charge they were risking could turn into a murder charge (which could still have meant the gallows in 1962).
This is where the suspense begins, with alternating scenes of the manager and secretary trying to break out of their prison, and the gang trying to engineer their release without giving themselves up. There is great ingenuity in the plotting of this drama, far above the standard 'B'-film level. It is truly involving to watch a mortuary attendant announcing that they'll have to wait for the keys until he gets the coroner's report, while the two captives are only minutes from suffocating. And the same when the manager's friends briefly wonder why such a punctual man should have missed their lunch-date, but eventually decide it's not worth investigating. It is these little sub-plots that drive the story to such effect. But the surprise-ending is too masterly to be disclosed here.
Derren Nesbitt, a dead ringer for Richard Burton, both in looks and in the blend of charm and menace, is brilliantly cast as the dominant gang-member, persuading a nervous young Keith Faulkner not to cut-and-run and just leave the captives to their fate. There is no leading lady in the full sense, but Ann Lynn as the secretary makes the most of her few opportunities. (She was just divorcing Antony Newley at the time, over a little local difficulty called Joan Collins.) The script is generally convincing, except for the gossip between the two young charladies, which comes a little too close to a pastiche of downmarket girlie-chat (though the topical references to consumer advertising are significant), and the mortuary attendant is rather too plodding as the official who insists on following regulations.
