As I watch her pestering Mick the Aussie for a date I wonder how it ever came to this. Am I really looking at the same woman who only last year caused such a stir when she marched into the staffroom and aroused feelings that had lain dormant for decades? The new media studies teacher was the sexiest thing to happen to St Brian’s since the Year 12 production of Cabaret in 1989. The men loved her, the women were split.

But the brightest star has burned itself to dust. A year of drinking, snorting, shagging and very little teaching has left her bloated and desperate. Mick is losing his temper as Titz pursues him round the staffroom begging for another chance. “We were so good together,” she sobs.

The Friday night stragglers shake their heads and tut at the pity of it all. “What are you talking about?” he snaps. “So we got off our heads and had a naughty in the lift. Big deal! I mean, look at you!” He removes Titz’s clenched hand from his arm and bolts for the door.

Titz’s chest is heaving so heavily that I fear it might escape the white T-shirt into which it is so tightly packed. I notice her midriff is drooping over the top of her jeans, her navel piercings hanging like large teardrops.

Sandie McSniff, head of PSHE, is scornful. “Well, my dear, what goes round, comes around. What was it you told me that night in the Horseshoes? Oh yes, that I looked like Jackie Stallone in a wasp’s nest. Well who needs the plastic surgeon now, eh?” Sandie’s view is fairly representative of the female section of the staffroom: Titz is a gender traitor who’s got what she deserves.

But it isn’t just her reputation with the staff that’s taken a nosedive.

Her Year 12s, once so delighted to have a teacher who wore proper clothes and did a bit of E at the weekend, have had enough of being randomly drug tested while a spaced-out Tiziana staggers around the common room cadging cigarettes. Ramona Lynch organised a petition asking if they could have a teacher who wasn’t pissed so often.

I feel sorry for Titz. After all, we did go on holiday together last spring, even if she spent the whole week chatting up the sunbed attendants while I got on with my lesson plans. “Come on, Titz, let’s have a drink,” I say and put my arm round her shoulder.

As we enter the Horseshoes, Orlando Jones and the drinking club nudge each other and snigger. “Oh look everyone, it’s Marianne Faithfull!” someone shouts to raucous laughter.

Before I can stop her, Tiziana has ordered two doubles of house vodka.

“It’s all such a mess, Charity,” she croaks.

“Oh come on, things could be worse,” I say with mock cheerfulness. “You could have slept with Orlando!”

“I tried to,” she sobs. “He turned me down. Orlando bloody Jones turned me down!”

The laughter from the bar suddenly sounds louder.

Charity Casement is the alter ego of a north London secondary school teacher. Next week: The return of Judith Crock.Charity Begins: Adventures of an NQT, Charity Casement’s diary of her first year at St Brian’s, is available from TES Books, pound;2.99. Tel: 0870 444 8633 or visit the TESBookshop at www.tes.co.uk