“Hello, Locum Recruitment. My name is Arlene. How can I help you this morning?” The greeting is irritatingly chirpy and barbecue crisp with antipodean positivity. I tell her my name and school and she thanks me on first-name terms like a sister. I explain my predicament: three days before the end of the autumn term I receive a last-minute resignation. Class teacher. Year 6. It’s complicated. I have no choice but to accept. Sats are around the corner. We need a replacement for two terms.

Arlene assures me that she has lots of teachers who fit my profile. It would give her the greatest pleasure imaginable if she could email me some CVs.

I dial the next agency. This time, a long-lost brother from Johannesburg.

Over the next hour, my inbox is filled with more than a dozen CVs from a clutch of agencies. One is five pages long, listing work at school after school across the capital. Short stays of a few days. I bin it.

Another prospective substitute worked at a burlesque nightclub and taught classes of 60 in Africa using just a blackboard and a piece of chalk. Yet another plays the bassoon to grade three. Another was formerly a cheese-processing operative. Amateur dramatics is listed in all of them.

By the end of the morning I have a long shortlist. I book the favourites for the first four days of term, with a simple brief of preparing two lessons for me to observe. In each case, I soon abandon my observation sheets and wonder how they scraped through training. I book more hopefuls.

More lambs to the slaughter. I send one home at lunchtime. The teacherless class begins to get restless. I prepare myself for the parental backlash.

Finally, like the 291 bus at home-time, two come along at once. Both are strong, dynamic and engaging. One hasn’t been told that there is a long-term placement at stake. He asks a colleague if it’s usual to be observed four times during a one-off supply day. The other entertains me with the story of how he fell out with his previous head and had to resign.

His story clinches my decision.

In all, I’ve seen nine supply teachers. The standard has been depressingly poor. I make a new year’s resolution to avoid supply teachers like the plague. Sadly, staff absence suggests that the plague is already here and I’ll have no choice.

I telephone my new-found sister at Locum Recruitment to negotiate a finder’s fee. Impossibly, my news cheers her up. Predictably, her finder’s fee brings me down. I think she has added a zero. I query her figure, on a first-name basis.

She repeats the same figure and I hear the smile in her voice. “Supply and demand,” she chirps.

Colin Dowland is the acting head of a large junior school in north London