But the ban appears to have been an oversight and the executive plans to amend its legislation to create a school exemption when the law is next reviewed.

Around three-quarters of Scotland’s secondaries are thought to have carried out the experiment, using a simple device made from a fitted pipe and a lit cigarette, to demonstrate the effects of smoking on the lungs. Under the new laws, teachers face prosecution if they carry out the demonstration under normal classroom conditions. The legislation allows them to do the experiment in a specially designated “smoking” laboratory or outdoors.

The Scottish Schools Equipment Research Centre argues that conducting the smoking machine test could actually be more dangerous to pupils’ health if smoke was blown their way on a windy day.