So where were you on Monday night?

It's claimed 21m people watched 'Panorama' on Monday: but all we know for certain is that 20,000 did. Welcome to the curious world of broadcasting, where the push of a button on a little black box can launch a career, and a single complaint can end one. By Jim White

A radio talk show host of some national eminence began his career operating the phone-in on a local station between two and four in the morning: a beat known in the business as the graveyard shift. As he nattered on about this and that, he would occasionally glance at the computer screen on the studio table in front of him. On to this screen the telephonist would type the details of callers ringing the station, anxious to air their views, things like: "Line 8: Dave from Dagenham. Subject: Who do them geezers in Brussels think they are?" Except that, no matter how many times he said "I know a lot of you are calling, but just be patient and we'll get through to you as soon as we can" the screen in front of him remained blank.

Wondering whether his job entailed little more than extended therapy, talking to himself, he approached the station controller to ask for a breakdown of the listening figures for his show. And the station controller revealed that, at the last count, he had nearly 2,000 listeners. Astonished, he thought he'd like to know more about them, so that he could tailor his effort more directly: how old they were, what sex they were. No problem, said his controller, flourishing a sheaf of statistics. Of the 1,980 listeners he had accrued, 1,980 were male, 1,980 were of social group D and 1,980 were aged between 18 and 25.

"In other words," he recalled, "they'd asked a panel of people what they had been listening to, and one bloke had been listening to me. From that they had extrapolated the figures and reckoned that since he had, then 1,979 others had too."

On Monday night, according to official figures, 21m Britons watched the Princess of Wales shaft her husband on Panorama. A huge number, that: only Bet Gilroy's departure from Coronation Street has come close this year. From the experience of the talk show host, though, are we to assume that this might be a fantasy figure? According to the BBC's research department, the figures were arrived at like this: 54,000 households, selected to be representative of all social groups across the country, are equipped with a little black box which they place on top of their televisions. Plugged in to the aerial socket, this piece of kit also has direct access, via the telephone line, to a central data-gathering base in London, which records exactly what is being watched in each house.

Furthermore, on top of the box are a number of buttons. Every time a member of the household walks into the room to watch the television, they press their own individual button. The computer knows who is on the other end of which button and logs it, giving information on age, sex and social status of each viewer. To prevent the sample growing stale, box holders are changed every three or four months.

Fifty-four thousand households is a huge sample in market research terms; it is more than 100 times the number of voters canvassed for a political opinion poll. Nonetheless, all that we can know for certain is that on Monday night about 20,000 households were plugged in to Panorama.

"Of course, ideally everyone would have a box," said a BBC stats spokesman, "but the technology simply does not exist to process that sort of rush of data. We feel that the sample we have provides as sophisticated a level of audience research as can be delivered for the budget." But surely there must be circumstances when the sample cannot deliver accurate data. What happens when they come across a programme, like our radio talk show host's, which has no one in the sample tuning in?

"We never give a zero rating, we simply say that programmes fall below a certain level," said the spokesman. "Sometimes overnight education programmes get very low scores, but that is because they have been videoed and watched at more reasonable times, information we can pick up on our video monitoring service. I have to say though that I have never come across a programme which no one in our sample saw." So someone watched The Late Show after all.

"Remember," he added, "the corporation has to feel confident in the information. This is not a PR exercise. Broadcasters need to know for their own purposes, to decide whether to commission another series of a programme."

This is the point. As hard as it may be to believe, broadcasters aim to provide the public with what it wants. In other media - books, newspapers, even satellite television - there is a simple, brutal indicator which tells you whether you have judged the public mood accurately: the market. If your product is wanted, it sells. Broadcasters on radio and terrestrial television, however, have to rely on far more inexact sciences. And viewing figures are the least inexact of them.

LWT's James Whale Show was severely reprimanded by the Independent Television Commission for a joke made by the Tory MP Jerry Hayes, which was found offensive by one viewer (see panel above). This single intervention altered the future editorial content of the show. And it isn't just Jerry Hayes who has had his broadcasting career checked by complaint power. Terry Christian was removed altogether from the employ of Talk Radio UK after one listener complained about an item on his Sunday night show (though at the time, it was unkindly suggested this represented three quarters of his audience; the other listener was a half-wit).

According to James Conway of the ITC, every complaint his organisation receives is investigated. "We look at the nature of the complaint and see whether there should be any action taken," he said. "For instance, we received a complaint on Thursday from someone unhappy with the interview with Anne Marie West on ITV on Wednesday. Not because they thought the particular programme was offensive, but because they thought the whole West case was so distasteful it shouldn't be given air time. In that case we felt no action should be taken."

But in others, whole editorial direction can change from the smallest number of objections. And it is not just sex or violence, people complain about the most unexpected things: a scene from Mr Bean which six viewers felt might encourage children to climb into tumble driers; a sketch from Hale and Pace which was thought by five people to be offensive to Catholics; or, at the other extreme, a scene from London's Burning which six viewers thought gave an inaccurate portrayal of paganism. Does this mean that, using the extrapolative techniques of other statistical gathering, 600 viewers were offended by the scene, but were too lazy to put pen to paper? "It's a reasonable rule of thumb that the more complaints you receive the more people were unhappy," said Mr Conway. "But not always."

Sometimes, as Mary Whitehouse's National Viewers and Listeners Association has learnt very well, a small number of complainers can make a vastly unrepresentative noise. If you are going to make a campaign complaint, however, make sure you don't give yourself away.

By far the biggest mail bag the ITC received this year was for the screening of Martin Scorsese's Last Temptation of Christ on Channel 4 (see panel above).

"We had a clue that someone was orchestrating that complaint," said Mr Conway, "because every single letter had the wrong post-code. Our address had been incorrectly printed in a magazine which suggested that if enough of its readers wrote in to us, the screening could be stopped. Of course, just because a pressure group orchestrates a complaint doesn't negate it. But you have to be careful in assuming it is a representative sample of viewers."

Sometimes the ITC acts without any complaints from viewers, as in the case of This Morning with Richard and Judy which, in August, was fined pounds 500,000 for product placement in a competition. And more recently action was taken on the over-explicit nature of programming on a satellite sex channel.

"Given the nature of the audience tuning in to that programming," said Mr Conway, "we were unlikely to receive a complaint if it was too explicit." There is, however, a group of people even smaller and even more powerful than the black box owners and the complainers determining what is shown on television: the television critics.

"The problem is," said one leading documentary producer, "senior commissioning editors don't watch television. They rely entirely on the buzz a programme generates to assess its worth. And since the only indicator of buzz they know is the critics, fantastic weight is given to their opinions."

This is, so insiders claim, one of the main reasons why British sitcoms are so poor. Sitcoms take time to develop, for character to emerge, for audiences to become familiar with their rhythm: the first series of Blackadder was, after all, a considerably less funny beast than the last. But critics, forced to review the first episode, are wont to find them unamusing. This, coupled with unspectacular viewing figures, mean they are generally killed off before a second or third series can be commissioned.

"Critics ought to be careful before slagging off a programme," said the anonymous source, "you may be preventing the programme maker from working again."

And, of course, from putting themselves at the mercy of little black boxes and lone viewers armed with pen, paper and a grievance.

Between January and October of this year, 4,047 people complained to the ITC about ITV and Channel 4 programmes. 1,500 of them took exception to the screening of Martin Scorsese's film 'The Last Temptation of Christ' on C4, making it the most complained about programme of the year. The ITC's attention was drawn to the fact that all 1,500 letters had the same, incorrect postcode on them. The complaint-in had been orchestrated by a religious magazine, which urged its readers to write, and then printed the address incorrectly.

Princess Diana's interview on 'Panorama' was watched by 21m Britons, the biggest audience of the year. Not a bad coup by Martin Bashir, that, since his programme's audience generally numbers no more than four million. We know this sort of thing thanks to an ingenious black box placed on the top of televisions in 54,000 homes across the country. From data received from that sample, extrapolations are made that are reckoned to be as accurate as any in the field of market research. Which is a bit like saying your car is reliable, as Skodas go.

On LWT's 'James Whale Show' last 18 August, the media-friendly Tory MP Jerry Hayes told a thin gag about a black mechanical toy cat. In October, the joke was deemed by the Independent Television Commission to be in breach of Section 1.4 (ii) of its programme code, the section dealing with offence in jokes of a racial nature. The programme's producers were advised that greater sensitivity in that area was expected in future, and Hayes was obliged to write a formal apology. The ITC moved into action because it received a complaint. From one viewer.