Linda was earning about £35,000 a year as a marketing manager until a minor car crash left her with post-concussion trauma and no career. For the past five years she has struggled to combat crippling migraines and constant pain while living on statutory sick pay, followed by benefits.

"From being a healthy, happy 39-year-old, I went to a doctor telling me in 2008 I had to give up full-time work or have a stroke. My employer put me on statutory sick pay after just over a week, though I did have [mortgage payment protection] insurance that paid my mortgage for a year," says Linda (not her real name).

"The problem was that, while my mortgage was paid and the SSP just about covered my bills, I was left with nothing for food and other outgoings. I had to see a chiropractor at £30 a time and was told I had to exercise but only under supervision, so I had to keep an expensive gym membership. Everything went on credit cards. I have run up £41,000 worth of debt due to my illness."

Linda is not alone in getting in financial difficulty after being ill. Employees are entitled to statutory sick pay (SSP), even if they have only recently started working, so long as they are off sick for at least four days in a row, including weekends, bank holidays and days they do not normally work and have average weekly earnings of at least £102. However, the standard SSP is just £81.60 a week (pro rata if you work part time) and is only paid for up to 28 weeks.

Many employers run their own company sick pay schemes: these must be at least equivalent to the SSP, but are usually much more generous, typically paying full pay for a set number of weeks, followed by half pay for another pre-determined period. The terms should be set out in the written statement of employment particulars, which should be given to the employee within two months of starting work. Employees who are still unable to work at the end of SSP or their employer's sick pay scheme can apply for state benefits.

As Linda has found, it can be difficult to make ends meet. "I had four credit cards that I didn't even ask for sitting in a drawer, so when things got tight, I started using them. I didn't really understand what I was doing. My injuries had made it impossible for me to think straight. I was buying food and everything on credit.

"After a year, my mortgage insurance stopped, but I was given income support to cover my mortgage and was shunted on to employment and support allowance as it's now called. I am allowed to work 15 hours a week and have to declare all my income. If I were to work longer, I'd face a reduction in benefit. The future is difficult. I don't know how I will ever clear such a massive debt."

According to research by Aviva, 52% of UK workers would be unable to survive financially for more than three months on statutory sick pay, with 30% saying they would manage for less than one month. Only 9% said they would remain solvent for a year or more.

Most people are not even aware of how much support they would be entitled to if they fell ill for any length of time. The research found 19% knew how much sick pay they would be entitled to, but 26% believed they would receive considerably more, with 16% thinking they would get double what they would actually receive.

Nearly half said that they would eat cheaper food, and 19% would cut down on heating to save money; 14% said they would have to move house.

Not surprisingly, 65% of those questioned cited financial concerns as the main reason to get back to work quickly if they were off sick, but regaining a sense of purpose (28%) was also a high priority. But 44% fear that going back to work could cause a relapse of their condition and 24% worry they will not be able to work to full capacity.

Steve Bridger, head of group risk, Aviva, UK Health, said: "Few people have the savings to support themselves and their families for long. Employment and support allowance can come to as little as £67.50 a week – less than SSP – which in many cases would hardly cover a family's food shopping, let alone their mortgage and other necessary expenses."

The insurance Linda had taken out on her mortgage was payment protection insurance, the policy which has been the subject of so many complaints to the Financial Ombudsman. Unlike many others, Linda was successful in claiming, but her policy was designed to stop paying after just 12 months.

By contrast, Kenneth Grose, from St Helier in Jersey, has been unable to work since October last year, and has been forced to take medical retirement despite being 48 – yet his insurance policy will pay out until he is 60.

In 2005 Grose was working as a parking controller when he was diagnosed with diabetes which led to peripheral neuropathy, causing chronic pain in his feet. The condition eventually forced him to take early retirement; however, his income protection policy from Aviva sheltered him from the financial implications.

"At work I would walk 12-16 miles a day in heavy boots, so once I developed my condition the job became impossible – there are days when I can't get out of bed because it's too painful to even put my socks on," he says. "I received statutory sick pay until I reached the point where I had to take medical retirement, but the income protection policy, which cost about £25 a month, began paying out at that point (it had a 13-week deferment period) and covers over half my former salary of £28,000. It will continue paying until my 60th birthday.

"I still have a mortgage to pay, I have a son I pay maintenance for, and Jersey is an expensive place to live, so without the policy my life would be very different. It's been a massive help. There are a few things I used to take for granted that I can't afford, of course, but I'm never going to be able to work again and no one can rely on state benefits, so I'm pleased I protected myself."

Income protection is an insurance policy that pays a monthly tax-free cash sum if you are unable to work through illness or disability. Payments normally continue until you are fit enough to return to work or reach retirement age, whichever happens sooner.

The policy can be tailored to start paying out when an employer's sick pay scheme comes to an end: this helps to reduce the premiums. It is also suitable for people who are self employed or not earning an income but fulfilling a role that would otherwise cost money to fill – such as looking after children.

Premiums can also be reduced by cutting the payment period or reducing the level of payout to cover particular payments, such as the mortgage.

The maximum level of cover an individual can buy is usually about half their current income, but as the payout is not taxed this could almost equal the salary of a higher-rate taxpayer. A greater percentage of cover can often be obtained through a company scheme: Aviva's group income protection policy offers up to 80% of normal earnings up to a maximum of £350,000 basic benefit.

"An ounce of prevention is worth a pound of cure," says Grose. "My illness has had a massive impact on my life, but so has my decision to protect myself. The policy has cost me over the years, but it's more than paying for itself now."

London and County has sponsored a free guide to income protection and life insurance.