This is a 23% increase in the past 10 years from 3.8 million, and over the last 12 months alone the number swelled by 174,000. This is a rise of 478 a day.

Analysis by Direct Line for Business has found that while 91% of UK businesses hire contractors for various projects, the majority (68%) require the contractors to have professional indemnity (PI) cover.

A fifth (21%) of UK businesses said it would depend on the type of work they would be undertaking for a firm as to whether PI is needed.

Nearly a fifth of business owners require the consultants to have PI cover over £1m and a further 34% (1.83 million businesses) expect anything between £100,000 to £1m.

The average level of PI cover expected is £715,000.

Jane Guaschi, business manager at Direct Line for Business, said: “An increase in the number of self-employed workers over the last few years means that competition among contractors can be a challenge. A contractor who doesn’t have the right PI insurance in place is doing themselves a disservice, as this analysis suggests it’s an important factor for businesses hiring contractors.

“Aside from the employment implications, professional indemnity insurance is an important factor for anyone offering advice or professional services. It can cover individuals and businesses for a range of risks such as if a client claims there’s a problem with any work which has led to financial loss or caused reputational damage. It’s also vital for anyone who has access to sensitive information or might infringe intellectual property rights.”

See YourMoney.com’s Going self-employed in 2017? A comparison of best business accounts.