Up to 10 million Britons or nearly a third of the UK workforce do not have secure employment, according to the GMB union, which has warned of a heavy impact on health and family life.

The union’s research, unveiled at its 100th annual congress in Plymouth on Monday, attempts to quantify people in what it calls precarious employment – those in the gig economy, on zero- or short-hours contracts, temporary workers, the underemployed and those at risk of false self-employment.

The data, based on a survey of nearly 3,500 people of working age, emerged before the publication this month of recommendations from Matthew Taylor, a former adviser to Tony Blair who was appointed by the current prime minister to lead a review into the gig economy. He is expected to recommend changes to the rights of self-employed workers.

Tim Roache, the GMB’s general secretary, said: “This paints a shocking picture of the modern world of work. Up to 10 million people go to work either not knowing what their hours are, if they’ll be able to pay the bills, or what their long-term prospects are. That’s a sorry state of affairs in the 21st century and a product of government’s failure to tackle bogus self-employment, the use of agency contracts as a business model and point-blank refusal to ban zero-hours contracts.”

Further interviews of those who identified themselves as insecure workers found that 61% had suffered stress or anxiety as a result of their current job and the same proportion said they had been to work while unwell for fear of not being paid, losing their job or missing out on future hours. The rapid change in employment practices was highlighted by more than three-quarters of those interviewed who said they had previously been in permanent employment.

A year ago, Citizens Advice warned that families were struggling to manage budgets and plan for the future as it estimated that a sixth of workers in England and Wales were insecurely employed.

Roache said workers were likely to suffer more if the UK economy slowed further, and the Treasury was being deprived of tax receipts.

Adrian Gregory, the chief executive of the London-based recruitment agency Extraman, who gave evidence to an MP-led inquiry into the future of the world of work in March, told the GMB that employment agencies’ use of tax-avoidance schemes was proliferating.

“Combining the money removed from workers with the money avoided in tax, an educated guess would be that around 15% of the total income of the recruitment industry is misappropriated. This would amount to around £4.5bn each year. I would think this figure is conservative,” he said.

He called on HM Revenue & Customs to set up a specialist unit to investigate rogue employment agencies and to tighten enforcement on holiday pay. He said industry estimates suggested that 70% of holiday pay, totalling nearly £3bn a year, was never paid.