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 are now employed on the controversial contracts, compared to 747,000 a year ago.
Women make up 55% of those on zero hour contracts, while one in five employed on them is in full-time education.
The Office for National Statistics (ONS) said that these figures show that almost three per cent of the UK workforce is on a zero hours contract.
New TUC analysis has shown that someone employed on a zero hours contract earns on average 50% less than the typical employee. The median hourly wage for zero hours workers is £7.25, while it is £11.05 for others.
TUC general secretary Frances O'Grady slammed the findings: "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."
A spokesperson for the Business Department hit back, saying: "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.
"Fewer than 3% of the UK workforce classes itself as being on a zero-hours contract in their main job, with almost 70% of those on this type of contract happy with the number of hours they work."
The contracts - which leave workers unsure of how many hours they will work each week - have been under the spotlight in recent days after Sports Direct said it would change arrangements for some staff.