This is the story of a statistic; it is sort of a detective story.

The mystery stat was sitting on one of our Times blogs and read “the average Brit is caught on security cameras some 300 times a day” and, God knows why, I just decided to chase the number down and find out where it came from. The colleague responsible for the blog referred me to a couple of news stories, and to a document issued by the office of an important and newsworthy quango.

One of the stories, sure enough, headlined “Friend or foe? The roadside spies cluttering up Britain” was published in The Sunday Times almost exactly two years ago, and referred “to the results of a study by the Government's privacy watchdog” (the Office of the Information Commissioner), which “found people were caught on a national network of 4.2 million CCTV cameras an average 300 times a day”.

The Evening Standard said the study stated that “the average Briton is caught on camera an astonishing 300 times every day”. It transpired that the document, entitled The Report of the Surveillance Society, was published in 2006 and had been praised by activists in the campaign against surveillance and what they see as the erosion of liberty. Its first line told readers: “We live in a surveillance society” and eight lines later referred to the fact of “CCTV [which] may capture our image several hundred times a day”.

The specific “300 times” claim occurred on page 23. The second part read: “There may now be as many as 4.2 million CCTV cameras in Britain: one for every 14 people, and a person can be captured on over 300 cameras each day.” The source was given in a footnote as coming from a book The Maximum Surveillance Society, published in 1999, by two academics, including a C. Norris.

So I set to work trying to find the book. In the meantime I mused on two things. First was how the “300 times” had become viral. It now occurs all over the place, and is the standard statistic used for the number of times Britons may or will be captured by CCTV cameras daily.

The second was the tendency for the statistic to mutate, as in the transformation from “can be captured” to the completely different “the average Briton is captured”. A British boy can have a baby at 13. That is clearly not the average age of first fatherhood. A New Statesman columnist had it as the “average Londoner going about his or her business... may be monitored by 300 cameras each day”, and a Daily Mail report that “it has been calculated that each person is caught on camera an average of 300 times daily”.

I managed to find a copy of the Norris book online. The footnoted page was towards the back of a chapter detailing a day in the life of a man called Thomas Reams, as he did various things in and around London. By the end “Thomas had been filmed by over three hundred cameras on over thirty separate CCTV systems”, the authors wrote, adding: “While this contrived account is, of course, a fictional construction, it is a fiction that increasingly mirrors the reality of routine surveillance.”

What? A fiction! A zillion (see footnote) references to “300 times” and it was a fiction!

Imagine, for a moment, that the original paragraph had read “and one hypothetical construction managed to have its fictional hero captured 300 times on CCTV in a single day”. It wouldn't be quite the same, would it? So I began to wonder how the ICO report's authors had failed to notice that an important factual source was fictional. Had they not checked it? The editor was a Dr David Murakami Wood, of Newcastle University, and the report had been commissioned by the Information Commissioner, Richard Thomas. Then I saw that Clive Norris, the Professor of Sociology at the University of Sheffield and author of the original work of imagination was a co-author of this report. This amazed me even more. He must have known, surely?

I contacted Professor Norris's co-author, Dr Wood. How, I asked, had such a thing happened? The report, he said, “was designed to help the ICO start a debate and to provoke policy discussion on the concept of ‘the surveillance society'... and it has”. He added, oddly, “there are probably all sorts of questionable things in it, in fact I hope there are many”.

Dr Wood's view was that the actual numbers were unimportant, that it would be “politically autistic to argue that if figure ‘x' is wrong, or a guess, or hypothetical, that this somehow undermines the import of those bigger questions”. In any case, he and his colleagues had tried to get journalists to understand the provisional nature of such statistics, but had failed: “Maybe that was our mistake - to overestimate the intelligence of the media.”

As to my precise point about noticing that a particular footnote referred to a non-real statistic, he recommended I ask Professor Norris.

Which I did. The professor told me that he hadn't written that part of the report, but was happy for his work to be thus cited. It was valid. True, Reams's camera quest had been an “imaginary journey [that] was a hypothetical possibility”, but all the systems in the story were real and could have been experienced.

Could have been, but you'd have to work at it. Reams is a City type who, rather unusually, lives on a drug-infested estate. He manages to visit two schools, the maternity wing of a hospital, goes to work, shops, is caught speeding in his car, crosses a level-crossing, parks in several car parks before switching to public transport. He goes to Heathrow airport, then a football match at Chelsea, after which he drives through London's most notorious red-light district (by mistake, I hasten to reassure the fictional Mrs Reams). His “could” is better paraphrased as “might conceivably”.

By way, I imagine, of justifying the report, Professor Norris reminded me that the viral 300 - still based on his book - entered the bloodstream long before 2006. And he was right. For example the BBC website carries a 2002 story stating that “the average citizen in the UK is caught on CCTV cameras 300 times a day”.

Another academic, David Lyon, in another book, Surveillance Studies: An Overview, stated that, when going about your daily business “it is likely that your image will be captured around 300 times”. But this weakens rather than strengthens Professor Norris's point. Dr Lyon, as it happens, worked with Dr Wood and Norris on the ICO report. If they knew the figure was speculative and had been widely abused and misunderstood why put it in?

I called the office of the Information Commissioner. After a few hours I was told that the report had been “elicited to start a debate”, its purpose was to “draw attention” to the problem, not to help to decide whether or not a problem existed. In a later statement the office referred to “earlier academic research estimates that a person can be captured on 300 cameras a day”, which reflected “the considered view of the author, who is an eminent expert in the field”. I also asked for a comment from Mr Thomas, the commissioner. There wasn't one.

So, that was the story of one statistic in one study. Every day we hear of several statistics, and every week of several studies. I have no idea whether the “300 times” case is typical, but I fear that it might be, and that, if only there were more time to scrutinise all the claims made in such “reports” - whatever side they take - we would discover many “truths” that just aren't. And I invite readers, if you come across any, to let me know, on david.aaronovitch@thetimes.co.uk

Times Recommends

• We have kit and leadership. Let’s go
• Behind the scenes at the biggest deal
• Conferences — what a waste of money