The number of people employed on zero-hour contracts has increased by 19% to 744,000 in the last year, according to figures from the Office for National Statistics (ONS). The number of people whose main employment comes from zero-hour contracts now represents 2.4% of all people working in the UK for April to June 2015, compared to 2.0% (624,000) of people for the same period the previous year.
However, the ONS says this may not be an accurate representation of the data, as people may be likely to report they are on a zero-hours contract because there is an "increased recognition of the term" rather than new contracts themselves.
The ONS added the figures show that people on zero-hour contracts are more likely to be women (54%), in full-time education (20%) and in both the younger and older age groups compared to people in full-time employment. The figures reveal 34% of people on zero-hours contracts are aged 16 to 24 and 6% are aged 65 and over, compared to 12% and 4% respectively for other employed people. On average, a person on a zero-hours contract works about 25 hours a week, with about 40% of people on a zero-hours contract wanting more hours.
In a separate report released by recruitment marketplace Glassdoor in August, about 45% of people on zero-hour contracts consider them exploitative, with 47% of unemployed people who were offered a zero-hours contract turning the offer down because it was not a guaranteed source of income.
The 19% increase figure comes from a poll conducted by the Labour Force Survey (LFS). However, the ONS also conducted a third survey which indicates there a 1.5 million people who do not have a contract which guarantees a minimum number of hours (NGHCs).
The difference between the ONS survey and the figures for the LFS will partly be accounted for by people who have more than one zero-hours contract with different employers or who have a zero-hours contract to supplement their main employment.
An ONS spokesperson added: "The estimate from the third ONS survey of businesses indicates that there are around 1.5 million contracts that do not guarantee a minimum number of hours, measured on work carried out in the fortnight beginning 19 January 2015.
"These latest results from the business survey can be compared to those for January 2014, published in April last year. Such comparisons provide, for the first time, an indication of the change in the number of NGHCs over a one-year period. This latest estimate of total NGHCs where work was done in the reference period is some 91,000 higher than the 1.4 million estimate for January 2014, an increase of 6%, though the increase is not statistically significant. As with the LFS figures, responses to the survey could be affected by changes in employers' reporting behaviour."
TUC general secretary Frances O'Grady says the rise in the number of workers on zero-hours contracts shows that Britain has a "two-tier workforce". She added: "People employed on these contracts earn £300 a week less, on average, than workers in secure jobs. I challenge any minister or business leader to survive on a low-paid zero-hours contract job, not knowing from one day to the next how much work they will have.
"Try telling zero-hours workers who have been turned down by mortgage lenders and landlords that they are getting a good deal. We need a stronger and fairer recovery that works for everyone, not one that forces people to survive off scraps of work."
Jon Ingham, of Glassdoor, said: "It's no great surprise to see the number of people on these contracts is on the up. The fact that many of those surveyed in the ONS study might not know what a zero-hours contract is could mean the scope of the problem is far greater than the figures indicate.
"With 255,000 of these contracts held by 16 to 25-year-olds, it doesn't feel like the best start in their careers. But for many it's all they know so they just get swept along and accept this 'pay-as-you-go' employment as the norm.