Teachers aren’t always what they seem. They haven’t spent their entire lives reading the Guardian and going on walking holidays in the Cotswolds.

They’ve got history, just like everyone else.

I’ve known for some time that Sandie McSniff, head of PSHE, has a past that includes various liaisons on hippy communes in the Sixties and a nude photo shoot for a radical feminist magazine on “the mysteries of the clitoris”.

God, I’ve even seen the pictures. John Baller is quite happy to regale anyone who will stand him a pint with stories of heroism and selflessness from his army days. He counts Andy McNab among his personal friends. And Orlando Jones needs little excuse to share his memories of treading the boards with Olivier and Gielgud at the Old Vic.

I had thought Harry Thomas was a closed book, but it turns out some of his pages are well thumbed too. Until recently he was known only as St Brian’s key stage 3 English co-ordinator, who for some unfathomable reason gets the best Sats results in the borough. Then the local paper ran a piece about how he played guitar in a Nineties indie band, A Herd of Wildebeest, who are back in the charts after one of their songs was used as the soundtrack on a TV ad for hamburgers. Apparently they played the early afternoon slot at Glastonbury one year. As a result, Harry has been transformed from school geek to coolest man in the staffroom. The tranquillity of his once exemplary classes has been shattered: when the kids aren’t taking photos of him with their mobile phones they’re demanding to know how he ended up in such a boring job as teaching. The Year 10 girls have started leaving notes in his pigeonhole.

Never one to miss an opportunity, the deputy head, Nigel Horsmel, has persuaded Harry and his band to perform a fundraising gig at the 13 Horseshoes as a warm-up for their forthcoming tour.

Monday night down the Horseshoes isn’t exactly the Mean Fiddler but there’s a respectable turnout, including Tiziana Fausti, Brenda Gache, Sandie McSniff and myself from the staff. Gareth and Gavin Gunner and a group of heavily made-up girls from 10C are sitting at the front of the stage squabbling over a bottle of Hooch.

Harry appears with his hair dyed blond and spiked up and wearing a tight black T-shirt. The performance is a shambles, brought to a premature halt when Gareth Gunner tries to crowd surf and succeeds only in slashing his forehead open on a mike stand, but Harry is magnificent.

Afterwards in the bar, Harry squeezes in next to me with a round of drinks amid much glaring from the other females. Blimey, I’ve pulled a rock star.

My track record with men at St Brian’s is not good. I’ve been stalked by a psychotic supply teacher called Graham Love, sexually harassed by Nigel Horsmel, and most recently duped by Blaine Harrington, a smooth-talking, snappily dressed metrosexual whom I mistook for a gay shopping companion.

Harry holds my hand but I’m nervous. “Harry, do you have any skeletons in the cupboard that I should know about?”

He leans over. “I’m afraid not, Charity. But I’ve got an old shirt that should fit you nicely.”

Charity Casement is the alter ego of a north London teacher. Next week: A new sponsor