SCREWFIX ANSWER (See first entry below)

In order to cease the daily hassle of the Spanish Postal Van dropping off more postcards with incorrect answers I have decided to now reveal the answer. The most popular reason given for the employees having to roll a dice at the end of their shift was that if they rolled a six they would have to make the tea. Very British! Actually, on rolling a 6 the employee is immediately searched by a colleague of the same sex. I think I might shop elsewhere in future...