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The number of people trapped on cruel zero hours contracts has soared by a fifth to nearly three-quarters of a million in the past year.

According to the Office for National Statistics (ONS), 2.4% of all people in employment are not guaranteed any hours of work.

This year the number has increased to 744,000, a 19% increase.

It's a huge increase on the 624,000 on zero hours contracts this time last year, which was 2% of the working population.

Women made up just over half those on the deals, which critics say exploits workers.

Number of people on zero hours contracts Office for National Statistics

And two in five people on the controversial contracts don't get as many hours as they want.

The figures also show those on zero hours contracts are more likely to work less than their usual hours of work than those in other types of employment.

On average, someone on a "zero-hours contract" usually works 25 hours a week.

But in April to June 2015, 15% of people on "zero-hours contracts" worked no hours in the week before their Labour Force Survey (LFS) interview compared with 9% of other workers.

TUC General Secretary Francis O'Grady said: “Zero-hours contracts are a stark reminder of Britain’s two-tier workforce.

“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."

People on zero hours contracts who want more hours ONS

Research by the TUC shows that average weekly earnings for zero-hours workers are just £188, compared to £479 for permanent workers.

It says Two-fifths of zero-hours workers earn less than £111 a week – the qualifying threshold for statutory sick pay.

Around 2 in 5 (41%) of people on "zero-hours contracts" want more hours compared with 12% of other people in employment, though this could be linked to a higher proportion of "zero-hours contract" jobs being part-time.

Looking in more detail, 12% of people on "zero-hours contracts" would like a different job with more hours compared with 2% for other people in employment (the remainder would like more hours in their current job or an additional job).

People on "zero-hours contracts" are more likely to be women, in full-time education or in young or older age groups when compared with other people in employment.

A third (34%) of people on "zero-hours contracts" are aged 16 to 24 and 6% are aged 65 and over (compared with 12% and 4% respectively for other employed people).

A fifth (20%) of people on "zero-hours contracts" are in full-time education compared with 3% of other people in employment.

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, in the fortnight beginning January 19 2015.

This latest estimate of total contracts without guaranteed hours 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.

This figure should not be directly compared with the last published estimate (1.8 million for the fortnight beginning 11 August 2014) to imply a decrease. It covers a different time of year and so differences in the number of such contracts reported may reflect seasonal factors.

A Business Department spokesman said: "Zero-hours contracts have a part to play in a modern, flexible labour market.

"For workers such as students and those with caring responsibilities they provide a pathway to employment, particularly when the individual cannot commit to regular hours.

"However we have acted to ban the use of exclusivity clauses in these contracts which prevent people from boosting their income when they have no guarantee of work.

"This is giving working people the freedom to take other work opportunities and more control over their work hours and income."

Unite assistant general secretary Steve Turner said: "The continued rise of zero-hours contracts underlines how government claims to be on the side of working people are nothing more than lip service.

"These figures are the tip of an insecure iceberg - they do not include short hours contracts and the wider rise in insecure, precarious work across the economy."

Chuka Umunna, shadow business secretary, said:

"These stark figures show that the Tories are the party of insecurity at work.

"Zero hours work is on the rise with the total number of contracts rising to 1.5 million and the number of people reporting their main source of employment as a zero-hours contract having risen by almost 20% since last year. At the same time, there are now over 1.2 million people working part time because they could not find full time work - 200,000 more than when the Tories took office in 2010.

"Ministers are watering down vital protections at work and have refused to act to protect workers on zero hours contracts. As long as ministers are happy to sit aside and encourage the proliferation of insecure work, more and more people won't have the security of knowing where their next pay cheque is coming from or being able to plan ahead."

How many people are on zero hours contracts in your region?

Region In employment on a zero hours contract Per cent of people in employment on a zero hours contract UK 744,000 2.4 England 645,000 2.5 North East 30,000 2.6 North West 88,000 2.7 Yorkshire and The Humber 53,000 2.1 East Midlands 65,000 2.9 West Midlands 79,000 3.1 East of England 64,000 2.2 London 96,000 2.2 South East 95,000 2.2 South West 74,000 2.8 Wales 40,000 2.8 Scotland 51,000 1.9