Some 4.82 million people are under the voluntary rate of pay that some employers give their staff, designed to enable workers to afford a basic standard of living.
The KPMG research found the proportion is much higher among waiters and bar staff, at up to 90% of workers.
The living wage rate is £8.30 an hour in London and £7.20- outside. This compares to the national minimum wage rate of £6.19 an hour.
The research found that over four in ten low paid workers say their finances are worse now than they were just one month ago.
Video below from The Living Wage Campaign calls for every worker in the UK to earn enough to provide their family with the essentials of life.
Marianne Fallon, head of corporate affairs at KPMG, said: "This research lays bare the extent of the problem of low pay in Britain.
"At KPMG we have found that the improved motivation and performance, and the lower leaver and absentee rate among staff in receipt of a living wage mean that the cost is offset and paying it is the right thing for our business."
She added: "Paying a living wage makes a huge difference to the individuals and their families and yet does not actually cost an employer much more."
Rhys Moore, director of the Living Wage Foundation, said: "Paying a living wage makes a huge difference to the quality of life of thousands of cleaners, caterers and security staff across the country.
