Around 320,000 people have a second self-employed job, according to figures released by the Association for Independent Professionals and the Self-Employed (IPSE).
This figure is significantly lower than the estimate given in research published by the University of Reading in 2018, which suggested 25% of adults in the UK run at least one business project alongside their full-time job.
The Reading review of more than 500 business leaders and 1,100 UK adults predicted that this style of work could increase to as much as 50% of the UK population by 2030.
Nearly three-quarters (73%) of those interviewed saw starting a business alongside their main job as a way to "follow a passion or explore a new challenge".
This view is shared by Chloe Jepps, deputy head of research at IPSE, who said the majority of people with a side hustle are "making a choice to fit work around their lifestyle and dreams".
"The internet has enabled more varied working, connecting people with ideas and opportunities.
"Part-time self-employment allows people to be innovative and take some risks, starting businesses that could grow into a great success."
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