Alan Davison is headteacher of a large London secondary school. Playing a significant role in the lives of 1,500 young people is quite a burden, but it is not the only one he shoulders. Mr Davison combines running Mill Hill county high with being a distance-learning tutor for Leicester University. “Heads are underpaid for the work they do,” he says. “I do my second job out of interest, but also for the cash it brings in.”

Mr Davison says many teachers - including members of his own staff - have two jobs. One of these is Angela Moore, a 27-year-old dance and drama teacher at Mill Hill with “student loans coming out of my eyeballs”.

To pay off debts of more than pound;5,000, run a car and “afford to do anything other than just pay my rent”, Angela works on Saturdays as an estate agent. A day driving around north London showing properties to prospective tenants earns her pound;50.

“I don’t feel that bitter about it. I’m used to it,” she says. “I’ve worked on Saturdays for years now and not questioned it. It doesn’t affect my job because I don’t let it, but it does make me feel tired. I don’t actually get a day off because I have to do schoolwork on Sundays.”

Angela has been at Mill Hill for two years and earns pound;18,000. “I’m young. I don’t have a family and I don’t have ties. If I did, I don’t know how I would cope,” she says. Of all her university friends, the only one with a full-time job who also works on Saturdays is a teacher.

The debt that forces some teachers to get a second job appears to be a growing problem for new entrants to the profession. It’s a worrying problem for the Teachers’ Benevolent Fund, which last year handed out pound;500,000 ingrants to impoverished teachers.

“We see a lot of cases of newly-qualified teachers in financial hardship,” says Mona Vadher, the TBF’s head of welfare. “They are often saddled with bank loans in addition to student loans. If they are supporting a young family or are mature entrants, it can be difficult.” Some try to cope by moving to a cheaper area, she says. Others take on extra lunchtime duties or extra marking, some even take in a lodger.

It’s difficult to pin down just how many teachers are moonlighting. For professional or tax reasons, many refuse to admit to it. Driven into this double life by lack of money, they find their cause damged by high-profile scandals such as that of Claire Norman, the Nottingham teacher sacked after her bosses found she had been working as a prostitute. The Sun newspaper revealed in July that her night-time career could earn her pound;2,000 - the equivalent of the threshold pay rise - in just seven days.

One young Warwickshire primary teacher has four years to go before she can even apply for her pound;2,000 rise. She makes ends meet working as a waitress on Saturdays and doing private coaching during the week. “I live on my own. I’ve got my own house. I’ve got a car to run and bills to pay. I just wouldn’t be able to survive on my wages,” says the teacher, who wants to remain anonymous. “I’d like to be able to give up waitressing and do other things, but I can’t. Some weeks I do try to finish early, but then I miss the money and wis I’d worked those extra hours.”

Now in her third year, she earns about pound;18,000. “Teachers’ wages are atrocious,” she says “I’ve got a friend who graduated at the same time as me who works in the car industry. She earns pound;3,000 a year more than me and when she comes home at5pm, her time is her own.”

The largest teachers’ union in the US, the National Education Association, estimated in 1999 that nearly half of teachers had a second source of income. And in Ireland in 1996, revelations over the extent of teachers’ moonlighting caused uproar.

The UK’s National Union of Teachers, which sought evidence of moonlighting in the late Eighties to support a pay claim, does not know how bad the situation is today. According to the Office of National Statistics, 26,000 teachers (or 4.2 per cent of the UK total) declare themselves as having two jobs. This figure could be more than accounted for by the number of practising teachers who work as examiners - 40,000, according to the Joint Council for General Qualifications. But many teachers may not regard such work as a second job, seeing it as a natural extension of their classroom work.

For one teacher, becoming an examiner was just that. But it was also a source of much-needed cash. Margaret Chapman, a 33-year-old senior teacher at Mill Hill county school, was facing huge child-care costs - more than pound;1,000 a month when both her children were at nursery full-time. “My husband earns a good salary and I was working as a head of department at that time. Even so, we still had an overdraft for a year,” she says.

“I was not going to give up teaching when I had children, but when you look at all the hours you put in and what you get back at the end of the month, it’s frightening.”

Margaret Chapman took on lunchtime supervisory duties and worked as a regional moderator for the Edexcel board for five years, earning between pound;600 and pound;800 a year after tax. She loved Edexcel and the work, but it was demanding. There were two months of intense activity every year “when you have piles of coursework in your conservatory” - plus, she guided heads of department in other schools through the coursework process. She gave it up “to concentrate on living. And I was made a senior teacher in September and I am doing an MBA, so something had to go. You need to be able to give 110 per cent if you are in a senior position.

“I work every weekend. I wouldn’t change my career for anything, but if you are a teacher bringing up a family without the extra money that responsibility points bring, I just don’t know how you survive.”

Survival - at least in terms of paying the mortgage and going out occasionally - for another Warwickshire primary teacher depends on private coaching. Now in her thirties, the teacher, who does not want to be named, has been doing this kind of work on and off since leaving university.

She charges around pound;10 an hour, but the coaching eats into her weekends and evenings. “Afterwards I go home and juggle getting something to eat, having a social life, planning, marking and all my ordinary teacher things as well as preparing for the next private session. Much as I love teaching,I don’t relish having anextra two hours’ work at the end of the day.”