The ONS has revised its estimate from 200,000 to 250,000 people at the end of 2012.
If an employee is on a zero hours contract they have no guarantee of hours and workers are only paid for the hours they work.
Labour has called on the Government to commit more resources to a review currently being conducted by Vince Cable's business department.
In a statement, the ONS said: "Following a review of the methodology used to produce estimates of the number of employees on zero-hours contracts, ONS has improved the way these figures are calculated so as to produce a more robust estimate. The effect of these changes is to increase the most recent estimate to 250,000 employees."
Spread like wildfire
The TUC said these updated figures still underestimate the true scale of zero hours contracts, which have spread "like wildfire" throughout the country.
"Some 300,000 workers in the care sector alone are employed on these insecure terms and conditions and that is before you factor in sectors like higher education, retail, legal services and journalism," said TUC general secretary Frances O'Grady.
"From Buckingham Palace to Sports Direct, zero-hours contracts are cropping up everywhere and the Government's oft mentioned review must lead to proper regulation to prevent their continued misuse.
"Employers cannot be allowed to take advantage of the current economic climate to employ people on the cheap."
Ian Brinkley, director of the Work Foundation, said the new figure was still a "severe underestimate".
"I think we know far less about this than we thought and the more we dig into this, the bigger the problem becomes," he said.
"I think we've exhausted what we can do with the statistics and need to start looking at what can be done to change it, with either a review or a select committee inquiry."
