It could be a day in the life of any local comp. But, for the Doctor, it is a clear that it is time to again jump in to save the world.

In the latest episode of Dr Who, to be shown on BBC1 this Saturday, the travelling Time Lord and his companions are at the fictional Deffryvale high, investigating the mysterious disappearance of several pupils. They quickly discover that all is not as it should be.

Posing as a physics teacher, the Doctor finds that pupils are disturbingly well-behaved, and demonstrate a prodigious knowledge of his subject.

Such studiousness from Year 9 obviously arouses his suspicions. “I thought they’d all be hoodies,” he said. “Happy-slapping hoodies with Asbos and ringtones.”

Meanwhile, his assistant Rose, played by Billie Piper, stumbles on canteen chips being fried in suspicious-looking oil by staff in gas masks.

Deffryvale clearly has no interest in the teachings of Jamie Oliver: a poster impels pupils to “eat more chips!”

This oil-heavy diet was instigated by Mr Finch, the evil-eyed headteacher.

Since the arrival of Mr Finch, played by Anthony Head, better-known for his roles in Buffy The Vampire Slayer and the Nescafe coffee advertisements, Deffryvale pupils have been getting record results.

But the ever-wise Doctor, played by David Tennant, proves what every teacher knows: results are not everything. With the help of K-9, the famous robotic dog, he uncovers a sinister plot to take over the world.

He then sums up the situation with what many teachers would say was all the skill of an Ofsted inspector: “Think how bad this could possibly be, and then add another suitcase full of bad.”

A spokeswoman for the National Union of Teachers said: “It’s extraordinary the lengths some schools will go to, to improve their league-table positions. But Dr Who won’t be on their side.”