Low wages, inflation and pay freezes mean that for more and more employees a second job is a necessity. But is having two roles necessarily a bad thing?

Meet Zoe Free, 24, senior recovery practitioner for Saccs, the charity that provides residential homes for children who have suffered trauma or neglect. Despite long hours, her job is highly rewarding. But like many of her peers in the charity sector, "reward" is more likely to be of the satisfaction than financial kind.

Free, who is based in Telford, gets a salary of "around £20,000". She says she loves what she does – but is feeling the pinch, not least because she's saving to buy a flat. For this reason Free now supplements her main job with a second one: at evenings and weekends she is a Zumba instructor. "I qualified a year ago, but the investment now means I earn £50-£60 per class, giving me an extra £100-£125 a week," she says. "Without it, I would struggle for the small things in life, like going out with friends. It's a real life-saver."

With inflation eroding take-home pay (in January 2012 alone, wages grew by just 0.7% compared to inflation of 3.6%), and with many families losing another £500 this year from cuts to tax credits introduced in the 2012 budget, Free's solution is increasingly becoming the norm. Last year 94,000 more people took on a second job, taking the total to 1.1 million, the highest level since 2002.

In January Unite found 24% of 1,500 Scottish workers it polled had more than one job. Of these, 90% were doing so to boost their main salary. Data compiled for the Guardian by recruiter PeoplePerHour.com found a 37.4% rise this year, compared to last, of people joining the site for a second job.

"A second job is almost becoming a must-have for some people now," says, Corinne Mills of consultancy Personal Career Management, and author of Career Coach. Mike Fetters, director at Totaljobs.com, says he's seen a doubling in applications for part-time jobs this year, saying the rise in second-jobbers is also due to people often taking two part-time jobs instead of one full time. In the three months to February 2012 alone, the total number of employees working part-time grew by 60,000, reaching 6.64 million, according to the Office for National Statistics.

But should we worry about this trend? Fetters thinks so: "Second jobs are often for financial reasons first," he says. "People often forget the career problems it could later create, such as a perception among employers that they are job-hoppers, unfocused, or hedging their bets between two careers."

Mills, however, argues that second jobs are now so common that employers should wake up to the fact, and even start helping their staff manage their dual lives. "Those who know their staff are on lower incomes should not be surprised if they are looking to supplement their salary," she says.

While Free says her boss has been supportive – even planning shifts around her classes for the first three months – some managers will no doubt wonder why they should accommodate an employee's other job.

But it's something they are actually responsible for. "Second jobs immediately invoke the Working Time Directive," says Carol Smith, senior consultant at employment law firm Croner. "Under their duty of care obligations, primary employers could be held responsible if illness or workplace accidents occur on their site, even if it's the member of staff's extra-curricular employment that causes them to work more than the permitted 48 hours a week."

Legally, staff must have 11 hours' break in any 24-hour period, and no less than 24 hours' rest (other than sleep) over a seven-day period. Smith says it's for employers to create a culture that encourages staff to tell their main employer whether they have a second job. Many do not, fearing promotion discrimination or finding their performance comes under scrutiny.

Michelle Caines, 36, a marketing coordinator for fitness products firm GymCompany.co.uk, who has a second job as a personal trainer, says being open has been beneficial for both parties. "One of the reasons I was hired in the first place was because my boss knew I was a REPs-qualified trainer," says Caines, whose extra work tops up her salary by £300 a month. "There's an obvious benefit that having my own private fitness clients brings to the business. I'm more confident and knowledgeable about fitness and what customers need. It's win-win and part of my continuous personal development."

It's not only lower-income workers who are looking for second jobs. Research by WebEden, which builds websites for budding entrepreneurs, says the squeezed middle are just as likely to need extra cash. Of 1,000 workers it questioned this year, 25% said they were considering setting up a sideline, with home selling back in vogue. This time last year, Avon reported a 43% surge in women applying to sell its products, while Jamie Oliver's Jamie at Home brand, which launched in 2009, has more than 3,700 sellers.

For Stevenage based Julie Knight, a teacher and mother, home selling has become the perfect second job to meet rising costs and her need for more flexible working. "I wanted to see my children grow up, so in 2009 I joined [the direct selling firm] Kleeneze," she says. "It's been a phenomenal success. Last year I turned over £220,000 and earned £20,000. I'm now earning £2,000 every four weeks." Earlier this year Kleeneze found 58% of people it polled would consider taking additional paid work. Knight has been so successful, that what started as her second job (two days a week, around part-time teaching) has now become her main income. "I've dropped teaching to two days a week," she says.

Jamie Stewart, managing director of Kleeneze and chairman of the UK Direct Selling Association, says Knight is by no means an isolated case. "Direct selling is experiencing a real come-back," he says. "There are about 400,000 people employed in the sector now, 80% of whom work part-time or combine it with their main job. Pay cuts and rising costs are creating increased interest in it. We're seeing lots of inquiries from public sector workers who have seen their pay frozen."

Most employees who have more than one job do so for a limited period of time. Some, like Gemma Nannery, go back to firms that employed them in their student days. Nannery tops up her main job as a business administrator for a garden design company with five-15 hours a week at a local Pizza Hut. She says: "Pizza Hut was my first job and the money and tips I earn supplements my income by about a third."

For some second-jobbers, the extra work isn't just for money, but for enjoyment. Godfrey Dyan, a chartered surveyor of 37 years, took a film-making diploma and has been running Red Rose Video for the past eight years. His work includes following the mayor of Harrow one day a week. "I'd long been interested in photography," he says. "I entered my profession for stability; now I'm pursuing my interest. I'd encourage anyone else to do the same. I'm bringing new skills to both jobs all the time."

It's the same story for horse-mad lettings agent Julia van de Venter. She rises at 5.30am each day to muck out two stables in Bournemouth. The extra £80-£100 she earns enables her to follow her passion – keeping horses of her own.

Van de Venter says: "Without the extra money, I couldn't afford to keep them. I don't see my second job as work. It's a lifestyle choice. If I wasn't doing this, I'd still be up early going to the gym."

Dyan and Van de Venter both say they make their two jobs work for them by keeping their dual roles separate. But in some areas having a second job still raises eyebrows. Last month a Freedom of Information Act request by Radio Kent revealed 155 staff at Kent Police had other jobs in 2011 (up from 81 in 2010).

Having two jobs is a rising trend and it could become a permanent feature.

Kath Austin, vice president of human resources for Pizza Hut, says: "We welcome people from any line of work. Those who work for us that also have main jobs include dance teachers, quantity surveyors, nursery assistants and business administrators. It indicates people need to work more, but with us or other companies like ourselves, people can have two jobs, with mutually beneficial results."