Crispin Fisher, 43, makes a living out of being funny. He writes wedding speeches and stand-up routines, and also sells ideas to greeting card companies. He is hoping to set up an online publishing company in 2010 and has ventured into e-book publishing in the past.

But Crispin is also known as Mr Fisher, a supply teacher in secondary schools near Chesterfield, Derbyshire. “I do supply because I have two young children so I work around them while my wife works full-time,” he says. The comic writing isn’t always reliable, so supply teaching can bring in a steady income and work around his other commitments. “I usually try to work within 30 minutes of home, and most of my work at the moment is in two local schools.”

Supply teachers often bear the brunt of the very worst schools have to offer. Badly behaved pupils go the extra mile to make life hell for the supply teacher who is drafted in, often at very short notice to cover. On top of problem pupils, it’s colleagues who can really make life difficult for the temporary supply teacher. Staffroom politics can be a nightmare at the best of times, especially if you don’t have time to suss out which seat you most definitely should not sit in.

But what is rarely apparent to permanent teachers, too busy to notice the humble supply teacher hiding in the corner of the staffroom, is that the flexibility of supply teaching works to great advantage and is worth all the uncertainty. There are 51,000 supply teachers in England, and while many of them will be on the lookout for permanent work, a large proportion see it as a lifestyle choice and wouldn’t have it any other way.

John Dunne, director of Select Education, a teacher recruitment consultancy and supply teaching agency, says that the reasons teachers sign up for supply work are many and varied. “We have teachers with us at all times of their career,” he says. “Broadly speaking though, there are three distinct groups, differentiated by their age: the NQTs, teachers in the middle of their career and then retired teachers, who want to top up their pension.”

In the current economic climate, it’s more difficult than ever for new teachers to walk into a job straight after finishing their course, so supply teaching has become a viable and appealing option as they continue to look for a suitable first teaching job.

It also helps that NQTs are able to reach qualified teacher status (QTS) while doing supply teaching, as long as they reach the required number of hours within 16 months (although a number of teachers are petitioning to get this extended). Furthermore, doing supply work can be good for building experience without the responsibility of steering pupils through a whole year of their studies.

Art teacher Melanie Dueck always presumed she would work as a supply teacher, almost as an extension of her training, before taking on a permanent role. Ms Dueck qualified as an art teacher at home in Canada but came to England last year after graduating.

“In Canada, you don’t really get a job straight after school so I always assumed that was what I would do,” she says. “New teachers are swamped with work for the first three years. I like having less responsibility and it’s a way of easing into the profession.”

NQTs are advised to move schools after their first two years of teaching so they can learn from their mistakes and start afresh with a new group of pupils. Doing supply, if it works out at more than a few days at the same place, can be good practice for a budding new classroom teacher.

So far, Ms Dueck has “only cried twice” on the job. “A few weeks ago, I had a really unmanageable class,” she says. “One girl was screaming at me: `Shut up! shut up!’ The bell went off, but I told them they couldn’t leave until they tidied up the classroom as it was a complete mess, but the whole class swarmed around me and started screaming in my face. When they left I just couldn’t stop crying.” But this is just a small part of the job, says Ms Dueck and this experience is by far the exception.

Despite not actively looking for something permanent straight away, Ms Dueck is fully committed to teaching and wants to help teenagers access contemporary art and understand it. “I like working with teenagers and feel like I have an empathy with them,” she says. “I didn’t like school myself, but the art department was my sanctuary. I could go and play music and relax and be creative. I eventually want to create that for other people, because school is just as much about those kinds of learning experiences as the academic stuff.”

Teachers in the middle of their career usually opt for supply teaching as a way getting used to professional working life again after a break, typically after leaving to have a baby.

This group usually does supply as it allows them to work only a couple of days a week to make childcare more manageable or just to get used to working again after an extended period of time away.

“It’s a re-entry period,” says Mr Dunne. “And sometimes a supply job turns into something permanent. I don’t want it to sound too much like a commodity, but there is a bit of a `try before you buy’ attitude, and that is for both parties involved.”

Laura McGowan found herself in this situation when she kept being asked back to cover teachers’ planning, preparation and assessment time at the same London primary school. She now works there three days a week, which is a welcome break from the chaos that she had to face while constantly alternating between schools.

“If a teacher didn’t know they were going to be off sick for more than a day or two, there wasn’t always a lesson plan, so you had to make it up,” she says. “It’s especially difficult if there is only one class per year group and you can’t ask the other teacher.”

Ms McGowan is also halfway through her first novel. She spends a couple of days per week writing and attends a weekly writers’ group, but supports herself financially by teaching. Before turning to supply, she worked as a receptionist and office manager for a recruitment company in London.

“I like being in control of the classroom, rather than working as a receptionist or doing administration,” she says. “I was really bad at it, and I found it so boring. I love the challenge of doing something new every day. You walk in, you have to think on your feet and go with the flow. One day, you have to teach a lesson about the anatomy of an insect; the next day, you are teaching kids how to draw Aztec art. Time passes so quickly and the day’s done before you know it.”

There is a world of difference between writing and primary teaching: while one is mainly silent and solitary, the other requires an element of performance and looking after at least 20 other young children at the same time, often with noise levels that would drive even the most patient person to distraction.

How does Ms McGowan balance the two disciplines? “They are very different, but I find they complement each other really well,” she says. “On my non- teaching days, I do need to spend the morning reading or researching to try to gather my thoughts and get my brain to concentrate on one thing at a time. You can’t do that when you are teaching - you would get a riot in a matter of seconds.”

It is unlikely that Ms McGowan or Mr Fisher would find the time or energy to pursue their other projects if they were teaching full-time. Teachers might get constantly reminded to count themselves lucky for the amount of holidays they have each year, but they are the third most stressed workers in Britain, according to a survey by the Stroke Association last year. The average stresses and strains of daily life are quite enough for most teachers to manage, let alone the idea of penning a novel or setting up a new business.

Perla Ranalli left a successful career in marketing to do a PGCE in modern language teaching, but didn’t want her new job to take over her life. She originally turned to supply when nothing permanent came up and started working at the same secondary comprehensive in Tower Hamlets on a regular basis.

“At the moment I feel that it’s good for me to have a year or two not doing any planning,” Ms Ranalli says. As a result, her evenings and weekends are freed up. “I sing in a band and we have at least two rehearsals a week. On other evenings, I usually go to the gym or see friends. There is now a clear distinction between my private life and my work life. When you are a teacher, you carry the work home and there are no boundaries. I can see that with my full-time colleagues.”

Ms Dueck agrees. “I love the fact that at the end of the day, my job is done,” she says. “Living in London, there is so much stuff to do and I want to have the opportunity to do it, and not be tired all weekend and working in the evenings. It also means I have time to do my own painting.”

Julian Stanley, chief executive of the Teacher Support Network (TSN), says that supply teaching is seen as a good solution for people who still want to teach, but don’t want to be burdened with excessive demands. “There are certainly people who turn to supply teaching as a way of not burning out,” he says.

The TSN is contacted by 100,000 teachers each year, all of whom find their job too hard to manage, for whatever reason. At the same time, supply teaching holds its own particular problems. While part of the appeal of supply teaching is that you get to meet lots of people and work in different environments, this can be a strain and magnify other difficulties that arise from the teaching itself.

“Sometimes there is a sense of isolation with supply teachers, who have less time to form friendships and relationships at work,” he says. “For less experienced teachers doing supply, as with any of us starting out at a new job, it can be difficult to ask for what you need. Much depends on how they are integrated into the school. Some teachers can get very territorial and permanent staff tend to see supply teachers as having less status.”

There is also the financial impact, which faces anyone working on a freelance basis. “The financial implications of working on a temporary basis is the reason behind a lot of our calls from supply teachers,” says Mr Stanley. “While some teachers choose it, for others, it’s a last resort and they need help to sort out their financial concerns.”

Over the past year, supply work has been increasingly hard to come by and even experienced supply teachers have had difficulty securing regular work. The role of support staff in schools has changed in recent years, so that TAs and now cover supervisors have more responsibility. Cover supervisors don’t need to be trained teachers, so will be cheaper to employ than a supply teacher, even on a permanent contract. While they are not officially responsible for all aspects of teaching, many schools rely on cover supervisors to take last-minute cover and supply teachers are feeling the effects. At the same time, the number of registered supply teachers increased by more than 50 per cent over the past year, meaning that one in 10 of all teachers registered with the General Teaching Council for England now works as one.

Until last January, Mr Fisher could depend on three or four days a week, but then the SEN school he was working at started using TAs as cover. “Since then the majority of my work has come from two schools but it has been sporadic,” he says. “One of the schools is a large comprehensive that has a sixth form and employs three full-time cover supervisors so usually they only call in supplies if they have at least six staff absent. Since January I don’t think I’ve done a full week’s supply.”

Ms Dueck has also been finding it much more difficult to get work in the past few months. “I’ve done some work as a TA and as a nursery nurse for pound;8 an hour, just because I’ve been so desperate,” she says. “I also got a job as a mystery shopper that I found on (community site) Gumtree, but I couldn’t bring myself to go through with it. That would be rock bottom really. It’s so hard when you are a trained professional, to think about going back to waitressing or jobs where you earn such little money.”

When the job of cover supervisor came up at the school where she had been doing supply work, Ms Ranalli decided to go for it. Most supply teachers wouldn’t even consider becoming a cover supervisor, seeing it as a step down from their hard-earned QTS. But Ms Ranalli decided that working as a cover supervisor would enable her to get more teaching experience without the additional paperwork and responsibility, and still give her the time to devote to her singing.

“The main reason I decided to go for it was because I really liked the school,” she says. “Even when I was coming in as a supply teacher, there is an ethic of teamwork and I got a lot of support with the school. I developed a good rapport with the teachers and pupils.”

There may be less demand for supply teachers in schools and they are often employed to cover a subject or age group outside their specialism. But permanent teachers and pupils are left in no doubt of the benefits that a good supply teacher can bring. Very few classroom teachers are able to cover all bases at the same time and will have strengths and weaknesses in their own subjects that a supply teacher will be able to complement.

Ms McGowan spends so much of her personal time writing that she is more than competent with literacy lessons and her classes no doubt benefit from doing creative writing and poetry with her as their teacher.

At the same time, pupils tend to be more frank about what they don’t know with a stranger, and it can present the opportunity for a fresh start for pupils given the problem-child label early on.

Ms Dueck says that she quickly builds up a rapport with classes, who see her as approachable and often ask if she can come back. “I joke about teaching being the profession of tears,” says Ms Dueck, “but my pupils can be really sweet. I feel like I make a difference.”

Secret diary of a supply teacher

8.35: “Ah good. You’re here . ”. The words, `at last’ hang in the air unsaid as the cover administrator swiftly hands me a cover sheet. “You were down for registration .” she continues, admonishing me with a pained look, “but I’ll take you down to your first lesson in the science block now”. As the bell rings, she bustles off at great speed. “Quickly now! This way!”

9.00: The pupils are engaged with writing about solids, liquids and gases. “What’s your name, Miss?” one of the boys calls out. “Mrs West,” I reply with a smile. “Miss East?” asks another, “Miss North?” suggests a third, joining in the classroom banter. 9KJ are all sniggering now, eager for a bit of teacher baiting. I smile blithely and ignore them. A pupil sticks up his hand “Are you a science teacher, Miss?”

“Not exactly. I’m a languages teacher.”

“Why are you teaching us science then?” Good question.

Another pupil chips in: “She’s not a real teacher, Jack.”

Jack asks: “Are you a real teacher, Miss?” Here we go. Get so sick of this. I shouldn’t get so defensive, but the kids’ attitude towards supply teachers always manages to needle me. Well I am only human after all. Might only be a supply teacher, but if you prick us, do we not bleed?

“Where’s Miss Bell?” asks Jack.

“She’s been off for months,” the boy next to him remarks.

“She’s dead,” interjects a voice from the back and the whole class laughs.

“No, she was sacked,” says one of the girls, “she was caught drinking whisky in the prep room.”

“And she ate dog food.”

“Don’t be ridiculous!” I say.

“She did. She keeps it in that cupboard”.

I take a surreptitious peek into the cupboard. There is a large tin of Pedigree Chum in there. Hmmm . yet another teacher driven literally barking by a bunch of unruly kids?

• Jo West is a supply teacher in Cardiff.