Zero-hours contracts are found mostly in the healthcare, education and hospitality industries
More than a million UK workers are on zero-hours contracts with no guarantees of shifts or work patterns - four times officials estimate, research suggests.
A survey of 1,000 employers by the Chartered Institute of Personnel and Development indicated 3-4% of the whole workforce were on such contracts.
Some 14% of affected staff could not earn a basic standard of living.
A review by Business Secretary Vince Cable is already under way, amid union calls for the contracts to be banned.
Under zero-hours contracts employees agree to be available for work as and when it is required.
Figures from the Office for National Statistics last week suggested 250,000 workers are on zero-hours contracts.
They came as it was reported that part-time staff at retailer Sports Direct, and a number of London councils, were among those employed on such terms.
According to the CIPD research, firms in the voluntary and public sectors were the most likely to use zero-hours contracts than those in the private sector.
The industries where employers were most likely to report having at least one person on a zero hours contracts were hotels, catering and leisure, education and healthcare.
The CPID said one in five employers in the UK have at least one person on a zero-hours contract. This means they can be officially counted as employed, but have no guaranteed paid work and could be sent home from their workplace without warning and without having earned anything.
Fluctuating wagesWhile zero-hours contracts may suit many, because of the flexibility it allows, critics point out that the system can lead to fluctuating wages and a risk that managers may use their contract as both reward and punishment.
Among those employers who use the contracts, the average number of workers who are on them is around 16%, according to CIPD.
Based on these figures, CIPD calculated that between 3% and 4% of all workers are on zero-hour contracts - which would equate to a million people in the UK labour force.
The workers who took part in the poll averaged just under 20 hours a week and were most likely to be aged between 18 and 24 or over 55.
Separate research among 148 zero-hours contract workers showed that 14% reported their employer often or very often failed to provide them with sufficient hours to have a basic standard of living.
Some 38% described themselves as employed full-time, working 30 hours or more a week.
Flexibility for employersCIPD chief executive Peter Cheese said that the calls for zero-hours contracts to be banned "should be questioned".
"There does need to be a closer look at what is meant by a zero-hours contract, the different forms that they take, and clearer guidance on what good and bad practice in their use looks like," he said.
"Zero-hours contracts, used appropriately, can provide flexibility for employers and employees and can play a positive role in creating more flexible working opportunities.
"However, for some this may be a significant disadvantage where they need more certainty in their working hours and earnings... Zero-hours contracts cannot be used simply to avoid an employer's responsibilities to its employees."
The University and College Union said such contracts used among teaching staff denied them financial security or stability and students continuity.
Dave Prentis, general secretary of the Unison union, said: "The vast majority of workers are only on these contracts because they have no choice. They may give flexibility to a few, but the balance of power favours the employers and makes it hard for workers to complain...
"The growing number of zero-hours contracts also calls into question government unemployment figures."
Business Secretary Vince Cable said: "For some these can be the right sort of employment contract, giving workers a choice of working patterns.
"However for a contract that is now more widely used, we know relatively little about its effect... There has been anecdotal evidence of abuse by certain employers - including in the public sector.
"Whilst it's important our workforce remains flexible, it is equally important that it is treated fairly. This is why I have asked my officials to undertake some work over the summer to better understand how this type of contract is working in practice today."
But shadow business secretary Chuka Umunna said zero-hours contracts should be the exception to the rule and called for a formal consultation.
He added: "Whilst some employees welcome the flexibility of such contracts, for many zero hours contracts leave them insecure, unsure of when work will come, and undermining family life.
"The 'review' the business secretary has established into zero-hours contracts is clearly inadequate given the seriousness of this issue and the mounting evidence of the abuse of zero hours contracts."
Source: BBC News - Business http://www.bbc.co.uk/news/business-23570345#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
