Watching the BBC TV series "Life on Mars", the premise of which is that a time-travelling cop from 2000s England is transported back in time to the 1970s, where he is continually confounded by the politically-incorrect nature of policing at that time.

In one of the scenes, he is surprised to discover that one-way mirrors for police line-ups weren't in use then. Is this true? I always thought that one-way mirrors had been widely used by the police for this purpose for many decades.

  • You mention the use in line-ups, but they are also found in interrogation rooms (as mentioned in a comment by Darrel Hoffman). The latter use also includes a speaker system for listening, and allows authorized persons such as other police, prosecutors, or witnesses to monitor an interrogation from just outside the room without being seen by the suspect and without the expense of CCTV. You may want to clarify, as these are different uses and the title question could be read as including either.
    – nanoman
    Commented Oct 28, 2020 at 20:22
  • "Time travelling" - ah, with this and Ashes To Ashes you have many revelations to come :)
    – Alan B
    Commented Oct 29, 2020 at 14:22
  • These one way mirrors are common in some media on police, but not even with TV-cops there ubiquitous. Are we sure they are common in real life? The question is about UK? My nitpick doesnt invalidate the question: either way, a statement can be made about when mirrors where adopted, to the extent that they were.
    – mart
    Commented Oct 29, 2020 at 15:13

1 Answer 1


Surprisingly enough, in England, screens for identity parades did not come in at all until the late 1980s.

A poke around the British Newspaper Archive (paywall, sorry) found this article from Nov 1986, talking about the success of the £4,000 Merseyside Police had spent on "one of Britain's first two-way mirror systems" (presumably what we would call a one-way mirror), and this article from July 1987 where West Mercia Police would be "among the first forces in the country to introduce one-way vision screens" following "an experiment in which the screens were installed in some stations earlier this year". It's not quite clear when they became universal, but it suggests forces were starting to roll them out across their regions at that point.

There seem to have been other experiments at the same time; this July 1986 article notes the success of an experiment in secretly videoing a suspect who had refused to take part in an identity parade, and circulating that along with video of nine other men doing the same thing.

So, why had it changed? Following some high-profile mistaken identification cases, the Devlin Committee on Identification in Criminal Cases in 1976 looked into all forms of identification of suspects. They specifically considered one-way screens (para 5.55), which had been recommended by an earlier report but did not feel that "the problem of the nervous witness is grave enough to require this solution".

(The earlier report that recommended screens was the Thomson Committee on Criminal Procedure in Scotland, 1975, Cmnd 6218 (in para 12.07); I haven't yet tracked down a copy of that to see what exactly it said, but the Devlin report suggests that they recommended something very much along the lines of the modern one-way screen system. It's unclear if these approaches were indeed adopted in Scotland prior to being adopted in England & Wales)

The Devlin report recommended giving the guidelines for identification parades statutory force, which happened with the Police and Criminal Evidence Act 1984. This gave the Home Secretary powers to issue guidelines, and it is these new regulations which will presumably have established using screens, first as an experiment and then as a universal rule. This review outlines some post-Devlin changes, but focuses on video identification (authorised 1991, common from 2002, now pretty much ubiquitous) and does not say anything about why screens were adopted. I can't find anything specifically discussing it in Hansard, which is odd - it's the sort of thing you would expect to be announced there.

(A note on terms: identity or identification parade is the most common form in the UK, though the US "line-up" does also get used; they're the same thing. "Parade" is presumably from the military sense of assembling and mustering troops for a particular purpose - "sick parade", "pay parade", "church parade" - rather than implying a public event.)

  • 1
    Were these more common in other places at that time? Not sure how you'd figure out when they first came in use in interrogation rooms in, say, the US, but they've existed since at least as far back as 1903 apparently, or further back to the 1860's if you include the related Pepper's Ghost effect used in stagecraft. Commented Oct 28, 2020 at 17:46
  • 1
    @DarrelHoffman I wondered about that! Devlin doesn't say anything specifically, and I didn't come across anyone saying whether or not they were common elsewhere. I'd have vaguely expected a "widely used in America" if that were the case, but the absence of the comment isn't really evidence either way. Commented Oct 28, 2020 at 18:10
  • 2
    Is an "identity parade" what Americans would call a lineup? Commented Oct 28, 2020 at 22:27
  • 1
    @chrylis-cautiouslyoptimistic- yes, same thing. I had both terms in an early draft but seem to have lost it, so will add something back in - thanks for flagging. Commented Oct 29, 2020 at 9:30
  • 1
    I find this very surprising because those mirrors had been in use by police in the US for many years prior to the 1980s. It was, after all, invented in 1903. Commented Oct 29, 2020 at 14:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.