Almost 700,000 workers were employed on zero-hours contracts at the end of last year, while 1.8 million contracts did not guarantee a minimum number of hours, the latest statistics from the Office for National Statistics show.
Labour has launched new plans to outlaw the "exploitative" zero-hours contracts and bring in legislation that would guarantee employees the right to a regular contract after 12 weeks of working regular hours in practice with an employer.
But some have warned that changing regulations would harm the flexibility they offer to the labour market.
Here are arguments for and against zero-hours contracts, from a business chief and someone formerly employed under one:
The case for zero-hours contracts:
Dr Keith Hellawell, chairman of retail giant Sports Direct, defended his company's use of zero-hours contracts when he appeared before MPs last week.
Around 4,350 of the 19,000 Sports Direct employees are permanent salaried staff, he told the Scottish Affairs Select Committee, while the rest are "casual", working on an average for around 15 hours a week.
Such staff would be told on a Thursday their work roster for the following week and then could swap shifts or change arrangements.
He said: "The situation works for us, and up until quite recently we have had no complaints or criticism from staff."
Dr Hellawell said that a third of permanent staff had previously been employed on zero-hours contracts.
Four out of five of the non-permanent employees were under the age of 25 and were often university students or people who enjoyed the flexibility of part-time work, he added.
He told MPs that moving more staff on to permanent salaried positions would lead to fewer jobs.
The case against zero-hours contracts:
George Martin, 21, from Romford in Essex is a final-year student at Barking And Dagenham College. He is going to university in September and has a part-time retail job for clothing company Superdry.
Two years ago, when he was a first-year student, he worked on a zero-hours contract at Sports Direct in the Lakeside shopping centre in Essex.
He said: "I had just passed my driving test back then and needed money to pay for insurance and petrol. I was at college for two days a week and worked about four other days, doing the morning delivery shift."
Mr Martin's work pattern was different every week, he said. Shifts were around four or five hours and he worked for 15 to 20 hours a week, finding out his rota on the preceding Wednesday - sometimes four shifts, sometimes none.
But after six months of regular work it dried up, and he was left not knowing from one month to the next whether he had any work.
He said: "I got lots and lots of hours between May and December, then after Christmas that was it, I didn't get any. I kept going in and asking for hours and they said to come back and try the following month. It was only in March or April that they started giving people hours again.
"I went from 20 hours a week up to Christmas to having nothing for three or four months. It was hard. After Christmas I had to borrow from my mum and dad to pay for my car insurance and then hope to pay them back, and I couldn't plan things with my girlfriend or mates because I didn't know if I would have any money.
"When I joined I was 18 and it was my first job. I knew it was going to be a zero-hours contract, but I didn't think that I would get no shifts after Christmas.
"With my job now I get a specific amount of money and can balance it and save, and before I couldn't do that. I would never do it (a zero-hours contract) again now. I would recommend that people get a proper contract. Even if it is just for four or eight hours, at least you know you are getting a certain amount of shifts."
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