In the dining area of a school in central Scotland, the senior staff on duty were tense. They could sense something was not right. Of course, teachers are experts at picking up changes in the atmosphere. It might be due to a full moon or high winds, a football match or music event in the area, or simply rumours of a fight in the playground.

However, this was different. In one corner, third-years were hitting themselves over the head with plastic bottles, like a throwback to Jeux sans Fronti res. Some first-years were wrestling, trying to snatch small articles off each other. The pitch of the ambient chatter was a tone higher than usual, and louder.

Whatever the cause, staff knew they were dealing with excited pupils not best prepared for afternoon classes. The question was: how and why? Can you help?

Apparently, Crimewatch UK has a fairly high level of success as the programme appeals to viewers to solve mystery crimes, though it sometimes takes a few months to get a result. In the Case of the Excitable Pupils, the explanation was more easily reached.

Investigations discovered that catering services had launched a Coca-Cola promotion that lunchtime. If you bought a bottle of Coke, you could win one of a number of small prizes. The result was a vast increase in the number of bottles sold, the provision of plastic missiles for score settling and an outbreak of toy envy among younger pupils, leading to the wrestling matches.

Litter doubled, and teaching staff were faced with afternoon classes filled with pupils who had ingested far more e-numbers than usual and found it difficult to keep still. It is hard to credit that the school had no control over this unfortunate foray into commercial activity.

Clearly, catering services are not to blame; they are awarded a contract that instructs them at least to break even and, in any case, it seems a bit of a tall order to expect schools to fight alone against the huge weight of commercial exploitation that makes Scotland’s children’s diet a cause for real concern.

Finland has shown that concerted action can change a nation’s diet. If our Parliament really wants to make children healthier, it can consult and then enact legislation which makes it possible for local authorities, schools, families and support agencies to work together to achieve it. There is goodwill and good work being done, but the effort needs to be co-ordinated.

In the meantime, don’t have nightmares!