Although certificated by the BBFC in June 1961, this film did not get a release in the UK until December 1963, when it went out as the support film for Adeus, Amor (1963).
The famous film company Hammer invested a mere £37,000 by 2009 standards for the making of Estranho Assalto (1961). To optimize its budget the film uses a limited number of sets --- an interior street set, the trading area of a bank, the manager's office, the stairway between office and the vault, and the interior of the vault itself.
The screenplay was adapted from the 1960 Associated Television Theatre 70 (1960) teleplay The Gold Inside (1960) by Jacques Gillies, also directed by Quentin Lawrence, and featuring André Morell (Colonel Gore-Hepburn) and Richard Vernon (Mr. Pearson) in the same roles.
The wall calendar is changed at the beginning of the film to Wednesday, 23 December. The only year close to the release date of the film to which this applies is 1959.
Harry Fordyce's (Peter Cushing) reference to the bracing air on Dartmoor is actually a reference to the notorious prison situated there. He's suggesting that Hepburn will eventually be caught.