The number of workers on zero-hours contracts has increased by a fifth over the past year, official figures show.
Just over 900,000 people say they work on a zero-hours basis in their main job - up from 747,000 a year ago.
The Office for National Statistics (ONS) said its figures showed that almost 3% of UK workers are on zero-hours contracts.
The controversial contracts, under which workers do not know how many hours they will work from week to week, has been under the spotlight this week after retail giant Sports Direct said it would change arrangements for some of its staff.
Nick Palmer, from the ONS, said: “The estimated number of people saying they work on a zero-hours contract has risen by over 20% since the same time last year.
“It is likely though that some of the increase we are seeing is because public awareness of the term ‘zero-hours contract’ has continued to grow.”
Women make up 55% of those on zero-hours contracts, while one in five of those on the contracts is in full-time education.
TUC general secretary Frances O’Grady said: “Zero-hours contracts have become an easy way for bosses to employ staff on the cheap.
“There is no getting away from the fact that zero-hours workers earn less money and have fewer rights than people with permanent jobs.
“It is very easy for politicians and employers to talk about the ‘flexibility’ these contracts offer, but they are not the ones living at the sharp end of the labour market.
“If you don’t know how much work you will have from one day to the next, paying the bills and arranging things like childcare can be a nightmare.
“Today’s figures are a stark reminder of why we need to create more decent jobs people can actually live on.”
New TUC analysis showed that the typical worker on a zero-hours contract earns 50% less an hour than the typical employee.
The median hourly rate for a zero-hours worker is £7.25, while for all employees it is £11.05, the study showed.
A Business Department spokesman said: “As the Prime Minister has made clear, we want to do more to build an economy that works for everyone and to help working people who are struggling to get by.
“Since May last year, the use of exclusivity clauses has been unlawful, meaning that individuals have more control over their lives and can work more hours with another employer if they wish.”