The “worm” is an instant poll tracker which wriggles across people’s TV screens, showing the net negative or positive reaction of a small group of the public to what is happening on screen. Running a worm across a politician’s speech or a debate between politicians has become a not uncommon feature of political coverage across many democracies.

The worm has even occasionally surfaced in the UK – so will it surface again for our TV party leader debates at the general election? And will worms offer a chance for Channel 4 to repeat an Australian trick and put one over the other channels who have excluded it from the debates?

Known in the US as dial groups (because a group of people is each given a dial to twist towards positive or negative), worms have often been the cause of controversy there. Joe Klein in Politics Lost recounts how badly they got the 2000 Bush-Gore debates wrong:

The first debate was a classic example of the perils of dial groups. “The dials were terrific for us,” [Gore Press Secretary] Lehane recalled. “You could hear the guy who kept track of the machine calling out the numbers – 92, 78, 88 – fabulous numbers every time Gore spoke. Shrum and some of the other folks were, like, ‘The election’s over. We’re cleaning his clock.’ I had my doubts. I just smelled the arrogance thing happening.’

He was right about the smell – because the post debate reaction was highly critical of Gore for perceived arrogance. His campaign did anything but soar to victory after the debate.

One reason for the worm’s fallibility is that it only captures of the moment reaction. As Klein also wrote of another occasion,

If anything negative was said, the dials would plummet. This was, of course, computerized hokum: people might not like a negative message, but that didn’t mean they wouldn’t remember it and act on it. The dials could catch momentary reactions but not overall impressions.

However, the worm is great fun to watch – and there will be great temptation for one TV channel to put a worm on its coverage in order to get viewers to come to its channel. With the news so far that the footage from two of the three debates (BBC and Sky, but not ITV) being immediately available to other broadcasters, a broadcaster excluded from the debates could take the footage, add a worm and get the audience coming to it.

Indeed, this is exactly what happened in the last Australian federal elections, where one channel added a worm – to great controversy, with its footage being pulled part way through the live debate before being hurriedly restored from another source.

What chance Channel 4 or someone else trying the same here?