The inevitable and often repeated inquiry is set to ring out across the UK as schools break up for the summer holidays today. Now drivers on long, hot car journeys along Britain’s traffic-choked roads will be able to predict exactly when the little backseaters will first ask the question.

Professor Dwight Barkley, of the mathematics department at the University of Warwick, uses a number of factors to work out the equation, by calculating the time you finally get all the kids in the car and eventually leave the house, the number of children in the car and the on board activities to keep the youngsters occupied.

Prof Barkley explained: "Mathematics can help answer many of life’s questions and this equation can be a fun way to think about the problem of keeping children entertained."

The mathematical explanation is that the time it takes for a child to ask the question equals: one, plus the number of activities to do, divided by the number of children in the car squared.

To get the final answer, that figure is then added to the time it took the family to get into the car and set off on their journey.