Factual error: There is a phone ringing in the police office, but it is using the American style ringing tone - with a single, repeated, long ring - instead of the British ring tone - two short rings repeated. (00:00:24 - 00:01:17)
Factual error: Sam's watch (which we see when he checks it just after the escape attempt) is a quartz movement "analog" with a little window at the bottom where an LCD (Liquid Crystal Display) display shows the date. LCD didn't appear on watches or calculators for another five or six years.(Although in 1973, there were Digital Watches with LED (Light Emitting Diode) displays. (You can see Roger Moore as James Bond wearing one in "Live and Let Die"(1973)).
Chosen answer: Sam is using the modern wording of the right-to-silence caution prescribed by legislation such as the Criminal Justice and Public Order Act 1994. In the 1970s, the wording would have been different, if it was used at all.
Sierra1 ★