There’s a Christmas card in my pigeonhole. The front has a picture of the head, Dr Scarlett, with a speech bubble that says, “Happy Christmas! And remember, moderation is the mother of improvement!” Inside is a pound;5 voucher for Mr Burger, the local fast food joint and official sponsor of St Brian’s.

The sight of the burger logo brings back awful memories of last year’s staff Christmas meal, held at the aforementioned restaurant. Five cases of salmonella and an unfortunate incident involving two pissed classroom assistants and a member of the kitchen staff.

This year things are going to be different. John Baller has arranged a staff trip to Calais - pound;19.99 including coach fare, bowl of moules-frites and complimentary bottle of Bailey’s. It sounds dreadful, and Brenda Gache tells me the whole thing is a cover for John to smuggle back a load of booze for his Christmas car boot sale. But it’s either that or a day at home with my lesson plans.

I’m just writing out my cheque - rather curiously to “Baller Trading PLC” - when I get an unmistakable whiff of Blaine Harrington, my line manager and style consultant. I turn and smile. “Mmm, smells good, Blaine. What is it?”

He offers me his cuff to smell. “Salvatore Pheromone Pour l’Homme. My house boy has a contact in Grasse.” Then he spots my invite from Baller. “Oh dear, Charity, you can’t possibly go. I’ve got you down for the senior management team’s bash the same weekend. After all, you are a head of department now.”

“Yeah, can’t have officers mingling with the ranks, can we?” John Baller, union activist and Falklands veteran, rips up my cheque and storms off.

Blaine carries on, unfazed. “Anyway, we’ll go shopping tomorrow to get you something black and sexy. Oh, and Charity, get your hair done, there’s a love.”

On Saturday evening my cab drops me off in front of what looks like a stately home. A man dressed in a red waistcoat with gold braid answers the door and leads me silently to a mahogany-panelled room full of Queen Anne furniture and exotic wall hangings. I put my suitcase down on one of the four-poster beds as a woman emerges from the bathroom wearing a kimono.

It’s Amy Studds, the bursar. “Oh, it’s you,” she says, as she blow-dries her hair. “Your bed’s over there.”

I change into my new dress while Amy squeezes into a lace bustier and knicker set. “I’ll see you downstairs in the library for drinks,” she snaps and heads for the door.

“But Amy, your dress. You’ve forgotten to put it on.” She rolls her eyes theatrically. “Oh for Christ’s sake, Charity, it’s a party, not an Inset day. Loosen up!”

I arrive in the dining hall to discover every man in the room fawning over Amy. Blaine can’t contain himself. “Oh Amy, you’re just so Madonna! I know all her routines, you know.” They spend the rest of the evening giggling and dancing like a couple of kids.

Just as I’m beginning to think about bed, a waiter tells Dr Scarlett there’s a phone call from France. Apparently the staff outing hasn’t gone smoothly. Orlando Jones and Gabriel Mooney have been arrested for soliciting on the ferry, and the coach has been impounded by customs and excise.

Amy Studds appears from behind a chaise longue. “God!” she shrieks. “Don’t these people know how to behave?”

Charity returns on January 7