Foul sandwiches were the reason to evacuate a school in England

The students of one of the schools of Lincolnshire county smelled a very strong intolerable smell during a written exam. The teachers imagined that it was nothing but lethal gas and they gave the alarm. The exam was stopped, all students were evacuated, firemen arrived. The latter started examining the building until they found a bag of rotten sandwiches, which was the origin of the stench. The teachers thought that it was simply an attempt to derange the exam: a student was not prepared for it, and a bag of foul sandwiches saved him from the failure