The number of people who are self-employed has increased by over 730,000 in the past six years, but average income has slumped by 22%, a new study has revealed.
Around 4.6m people work for themselves, more than at any time in the past 40 years, said the Office for National Statistics in a report which does not cover Northern Ireland.
The number of self-employed over 65-year-olds has more than doubled over the past five years to almost half a million. The most common jobs are in construction and taxi driving, although there has been an increase in the number of management consultants.
Average income from self-employment has fallen by over a fifth since 2008, to £207 a week.
The TUC said income has "collapsed", with self-employed workers earning less than half that of other employees.
General secretary Frances O'Grady said: "Self-employment appears to be a key factor in the UK economy's shift towards low-paid work. Many people want to work for themselves, but the growth in self-employment is reducing people's pay, job security and retirement income, and is likely to be reducing the Government's tax take too."
Around 4.6m people are self-employed, 15% of all those in work, the highest since data was first collected 40 years ago.
Another 356,000 people have a second job in which they are self-employed.
Self-employment increased in the 1980s before falling during the early 1990s recession.
More than two-fifths of self-employed workers are over 50, working an average of 40 hours a week, although almost one in eight put in 60 hours or more.