The number of people setting up their own businesses has jumped by 367,000 since the start of the recession in 2008, according to official figures.
The increase - to 4.2 million - has mainly happened since 2011, with a rise of 219,000 in the year to 2012, the Office for National Statistics said.
The figures suggest that people who have lost their jobs in the recession are choosing to set up their own small businesses rather than finding another job with an employer.
The rise was fuelled by a big increase – 431,000 - in the number of self-employed people working on their own or with a partner. But the number of people running larger businesses with employers working for them fell by 66,000 over the same period.
The rise was spread across all parts of the UK, except Northern Ireland, where the number of self-employed workers fell.
The study also revealed that the self-employed work longer hours, tend to be older and are more likely to be male, than other employees.
The average age of self-employed workers was 47, compared with an average age of 40 for the UK's 25 million employees. Most (70 per cent) of the self-employed were men.
The most popular occupations for self-employed workers were taxi driver, construction worker, carpenters, joiners and farmers.
Almost six out of ten (58 per cent) self-employed people use their home for work, with most living in London and the South West.
The lowest proportions of self-employed people were in the North East, Scotland and Yorkshire and the Humber.