"Ah, and a very valuable role that is," he says, sensing Steve's sheepishness. "After all, with so many children in the building, it would be terrible if there safety couldn't be guaranteed."

"I taught Transfiguration," he says with something almost like mischief in his grin. "The art of using magic to turn one thing into another. It's a shame it's not really something practical to teach here in terms of subject matter, but it's given me a reason to explore maths and science further than I would normally."