And the good news is that starting up a business on the side is easier than ever before. It's not always true that it takes money to make money. In today's connected world, there are dozens of possibilities for online businesses that can be set up on a shoestring and run part-time. Indeed, recent research from Direct Line for Business has found that eight million of us are already doing so.
And more such 'bedroom businesses' are appearing every day, according to jobs marketplace Freelancer.co.uk. Earlier this year, it carried out a research study which concluded that the number of new spare-time start-ups rose by a third over the previous year.
And, the study found, the average start-up cost of such a venture was just £325. Respondents gave a number of reasons for the low cost, but the main two are obvious: the lack of need for office space, or for retail space when selling online.
"Starting a microbusiness online is easier than ever, and is less risky with small start up costs," says Freelancer.co.uk European director Bill Little. "Many of the people in this study set up businesses alongside their own jobs, hiring in freelancers for short projects to help get the business off the ground, before leaving their job to run the business full time."
1. Sell something home-made
There's been an explosion in the quantity and quality of hand-made goods available in recent years, and all thanks to the internet. It's no longer necessary to open a shop or secure deals with retailers: just create a website and start selling. Making it even easier are sites such as Etsy or Not On The High Street, which act as a marketplace for your wares. Costs vary from site to site, but can involve a joining fee, a charge for each listing and/or a percentage of sales.
2. Online trading
You don't need to make something yourself to sell it online. So many people now make an income buying and selling on eBay that they have their own independent trade organisation, the Professional eBay Sellers Alliance (PESA), whose members are turning over more than $400 million a year. Some make their money by cutting out the middleman, buying goods from wholesalers and selling them direct to the public. Others use their expertise to source, say, vintage clothes or antiques cheaply and sell them on at a profit.
3. Become a freelancer
Many specialist jobs are now routinely put out to freelancers working from home. Particularly in demand are technical skills such as website design, programming and software development, along with graphic design and marketing. Numerous agencies exist to match freelancers with jobs, including Freelancer.co.uk, Freelancers.net and People Per Hour.
The advent of video calling services such as Skype has made it far more practical for teachers to offer lessons online. There's a rapidly-growing market for English as a Foreign Language (EFL) teachers, who can sit at home and tutor children halfway round the world - it's particularly popular in China, Korea and Japan. Some of the bigger players are Englishtown, Telelangue and GlobalEnglish. Teachers can set their own hours, and many go on to set up their own small online schools.
5. Become a virtual PA
These days, there's really no need for a PA to be in the same town as his or her boss, let alone in the same room. There's also an increasing demand for part-time secretarial or admin support. As with teaching, there are several agencies that offer such virtual PA services, but many people simply start up by themselves with one or two small clients. Unlike teaching, though, it can be hard to find work that fits round an existing job.
6. App development
Had a brilliant idea for an app, but lack the technical skills? If your idea's good enough, you won't need them. It's now possible to hire top-notch Indian programmers to design an app for you at a fraction of the cost in the UK.
7. Write an e-book
With the advent of ebooks, writers stopped needing to win agents and editors over - and self-publishing stopped meaning vanity publishing. Many people have a rejected novel under the bed, or a store of specialist knowledge just waiting to be written down. Publishing options include Amazon Kindle Direct Publishing, Smashwords and iBooks.
8. Start a blog
This isn't one for a quick return - very few blogs ever make any serious money, and those that do generally take years. But if you have something you're passionate about, it can be worth a try. Drive traffic to your blog using social media, search engine optimisation and internet marketing and eventually - with a bit of luck - it becomes possible to make money from advertising and affiliate links.
9. Start a membership site
If you're an expert in your field, you can charge a monthly fee for access to an information-based website. Successful sites offer articles, seminars and member forums and can become highly profitable.
10. Data entry
Not one for the faint-hearted, as the work can be repetitive and low-paid. It's important, too, to do your research before taking on work, as it's an area associated with a number of scams. But start-up costs are low, timing is completely flexible, and the only skill required is fast and accurate typing.