Almost two-fifths of UK workers now have a “side hustle” and the number is expected to increase to half of the adult population by 2030 as the trend grows at an unprecedented pace, according to new research.

Henley Business School said increased uncertainty about the security of work is one reason pushing people to run a business on top of their day job.

Half of all employees with a secondary income do the extra work because they need the money, the research found, but many also do so to follow a passion or explore a new challenge.

The study of more than 500 business leaders and 1,100 adults found that 45 per cent of side hustlers consistently work more than 40 hours a week, and a quarter work more than 50 hours a week. Thirty per cent of people work on their side hustle during holidays from their day job, the report said.

Of those that do have a business as well as a job, the business generates a fifth of their income.

Collectively, those side hustles generated £72bn for the UK economy last year, or 3.6 per cent of GDP, but the researchers said firms have been slow to adapt to the new way of working and risk falling out of step with the needs of their employees.

Over half of business leaders admitted that they have no policy on side-working, and no process to record and monitor these activities among their workforce.

The majority of businesses do not expect any significant increase in the trend over the next five years, which is a mistake, according to the report.

“With 25 per cent of adults side-hustling today, there is no way back,” said Professor Bernd Vogel of the Henley Business School.

“The genie is let out of the bottle. Those who are underwhelmed and under-financed by their work, but have the appetite, if not the confidence, to go it all alone as an entrepreneur, will not let the chance slip.”

Naeema Pasha, director of careers at Henley Business School, said that side hustles can give people a sense of control over their own careers but that some started a business because of uncertainty in their job.