Until recently, I made my living by working as a private tutor for a number of wealthy families. I taught lessons on a yacht touring the Mediterranean, at various richly appointed addresses in south-west London, and once on a private jet to Bermuda. (Perhaps more pertinent than my instruction that day was the lesson on tax evasion that my students’ father gave them during the flight.)

Welcome to the world of private tutoring - an industry that is unregulated and getting bigger. When I was at school, around 15 years ago, it was rare, and even embarrassing - something to help stragglers, not to reinforce privilege.

But today tutoring is different. According to research in 2009 by the Sutton Trust, half of state secondary pupils in London have received private tuition in some form during their school years - up from 36 per cent in 2005. Across the country, the proportion has seen a jump from 18 per cent to 22 per cent. The trust is about to publish figures for last year which are expected to show that despite the economic downturn, the enthusiasm for private tutoring remains undiminished. There are no similar figures for private schools.

Some teachers discourage tutoring. They argue that it increases the inequity - already huge - between those who can pay and those who cannot. Others welcome it because it can improve results. Still others take tutoring jobs themselves, pocketing fees of up to pound;70 per hour.

I had mixed feelings about tutoring - desperate for the cash, but occasionally uncomfortable with the practices of the industry. As demand for tutoring grew and parents felt pressured into securing every advantage for their children, it became clear that they were depending on tutors with very different qualifications, although most agencies require a minimum level.

I started tutoring after graduating with a good degree from a Russell Group university. Like so many arts graduates, I had no luck getting a job. Tutoring, with its flexible hours and fast cash, seemed like a sensible interim way to earn a living.

I began by working for an agency that charged parents pound;45 an hour - of which I kept pound;25. Most of my students - and all my regulars - attended fee-paying schools, and many were preparing for Common Entrance exams or GCSEs. It did not seem to me that the parents were unsatisfied with their children’s expensive schooling; tutoring was merely the done thing, like tennis lessons. Everyone did it.

My training was cursory, even though I had no teaching qualification. The director of the agency asked about my experience and I attended a training day that focused on etiquette rather than pedagogy. We were told to leave the door open while tutoring, to accept a cup of tea if offered, and to offer to take our shoes off. And I was asked to pay for a Criminal Records Bureau check. I put this off a couple of times because I was completely broke. Eventually, they forgot about it and put me on the roster anyway.

Compared with some tutors’ experience, this was a thorough vetting. Tim Digby-Bell, another tutor, told me he was given work solely on the basis of a phone call which determined he had attended the exclusive Radley College. The agency is a big one and claims to vet and train its tutors. Despite signing up to tutor English, Mr Digby-Bell was asked at short notice to tutor GCSE maths. As he puts it: “No check, no credentials. I just got a call and the next day I was alone with this kid for four hours, teaching him maths, which I’d never done before.”

He later found himself frantically Googling “how to solve simultaneous equations” on his iPhone in the loo of a smart Chelsea townhouse.

There are excellent tutors and good agencies. But there is no formal scheme of regulation or oversight, so it is hard for parents to sort out which tutor or agency best suits their needs.

One English teacher in London, who did not want to be named, says a tutor’s help, if they are ill-prepared, can be damaging.

“For GCSE, teachers do a lot of work setting up the coursework . so that (students) hit the success criteria exactly. If you’re going to be a tutor, you have to understand what the assessment objectives are and how to meet them,” he explains. “I’ve had one student who produced work that I can almost hear coming out of the mouth of some university student who doesn’t know what they’re doing . a bizarre mix of confused second-year undergraduate and struggling Year 10. This student should be getting a B. The essay got a D.”

Another English teacher in Scotland says it is not unusual to find tutors doing pupils’ homework. “Staff at my school have had short stories handed in to them by kids who barely recognise - usually - the difference between first and third person which is almost fit to be published.”

I felt that some one-to-one work with a tutor who knows their material was helpful for a struggling student. I loved some of my work as a tutor - especially in maths, where an hour spent approaching a problem from various angles could work wonders. Most of the children were responsive and engaging. If there was a problem with a couple of my regulars, it was only that they occasionally took my help a little too much for granted. One student I taught while sitting under a genuine Picasso used to say: “Why can’t you just do it for me?” With others the sense of entitlement was less explicit, but still there.

In my experience, when tuition is the norm and not a last resort, it can foster a sense of entitlement and an inability - or unwillingness - to work things out for oneself. There is even evidence that it can harm students’ abilities to perform well at university. Researchers from the London School of Economics found last year that state-school pupils perform better at university than privately educated students from similar backgrounds - and attributed this partly to the use of private tutors.

For some parents, getting into the right university is enough and private tuition throughout school is an accepted part of this. One of my pupils - a nine-year-old - asked her mother where she would go to university. “Oxford, Cambridge, Harvard or Yale,” the mother said, before turning to me. “What do you think?” I stammered that I thought it was too early to tell. But it was telling that neither the girl nor her mother had any interest in what she might study at these universities, nor what she might do with a degree earned there. It was educational aspiration divorced from education itself.

Janette Wallis, of the Good Schools Guide, calls tutoring “highly contagious” and says that “it can take real nerves of steel not to succumb when you find out that other parents in your child’s class have engaged tutors”.

Certainly Lynn Gilbert, a mother of four boys who attended a private school in England, felt this pressure. She hired tutors for her two elder sons, who were struggling in some of their maths topics, and for her younger two for general preparation for SAT - a standardised test for entry to US universities, where her sons intended to apply. She said that the maths coaching was very effective, but the SAT tutoring, apart from forcing the boys to look at the material, made little impact.

“I’m not a big believer in tutoring, and actually it drives me nuts that so many people hire tutors, which then puts the pressure on the rest of us to do the same to not disadvantage our children,” she says. “I fought the trend with my first two. My eldest, who had no tutoring, basically ended up with the same scores as the other three. One can never sort out afterwards what factors played into their results - but wouldn’t it be better to spend the time reading a book?”

My generation, on the whole, didn’t have to hire tutors to get into university. But given the pressures that Lynn Gilbert describes, perhaps we would have done if we were at school today. The irony is that for some of us, the only work we could find after graduation was coaching the next generation of school-leavers for their entrance into elite universities. It is difficult not to be pessimistic about their prospects, although private tuition is one growth area that their own experience will have prepared them for, in their turn.

Frances Hallett is a pseudonym.

Private tutoring in numbers

- 22% cent of students countrywide have received private or home tuition - an increase of 4% from 18% in 2005.

- This figure is almost twice as high in London, with 43% of students having received some tuition - up from 36% in 2005.

- The South East region is second with 28%.

- Yorkshire and Humber is lowest with 11%.

- 77% of those who received tuition did so in maths, up from 71% in 2005.

- 55% received tuition in English - no change from 2005.

- 30% were tutored in science - up from 20% in 2005.

- 12% in modern languages - no change from 2005.

- 49% of those who received tuition did so for help with a specific exam, down from 52% in 2005; 47% said they received it for help with school work in general; and 15% because they were really interested in a certain subject.

- 5% said they saw a tutor because they wanted to study a subject their school does not provide, up from 3% in 2005.

- 11% said they did not know why they had received tuition, up from 9% in 2005.

- Double the proportion of pupils from urban compared with rural areas say they have received private tuition (24% compared with 12%). This is a slight increase since 2005, when almost one in five young people from urban areas (19%) received tuition, compared with 12% from rural areas.

Source: 2009 survey of 2,447 11 to 16-year-old students in state schools by Ipsos MORI for the Sutton Trust.