A whopping 1.4 million people are stuck on exploitative zero-hours contracts and most are paid less than the living wage, official figures showed yesterday.

The Office of National Statistics (ONS) revealed that more and more employers are forcing people to be available for work but paying them only when they are called in to do so.

Zero-hours contracts do not guarantee any work — leaving workers with no guarantee of a wage.

Last year it was estimated that anything from 250,000 to one million workers were employed on such terms.

But the Unite union said that even the new 1.4m estimate, based on a survey of 5,000 firms, may be way too low with the real figure as high as 5m.

Further and higher-education workers are among the worst-hit, with lecturers guaranteed no hours and unpaid during holidays.

University and College Union general secretary Sally Hunt said: “Without a guaranteed income, workers on zero-hours contracts are unable to make financial or employment plans on a year-to-year or even month-to-month basis.”

And Unite general secretary Len McCluskey said the contracts left workers’ income “dependent on the whim of your boss.”

He called for stronger employment protection against abuses and for the government not to do business with firms that use zero-hours contracts.

Some contracts demand “exclusivity” — meaning a worker cannot take on work elsewhere when none is offered by the employer.

GMB general secretary Paul Kenny said that must end and called for a right to payment for “deemed” hours worked based on a three-month average.

“What is not yet recognised is the extent to which people working on such contracts are blighted in terms of getting credit, entering into rental agreements etc,” he said.

He called for tax measures against fat-cat bosses earning more than £1m a year to deter them from over-paying themselves — leaving more cash for workers’ wages.

The TUC said most zero-hours workers are paid less than the living wage of £7.65 an hour outside London and £8.80 in the capital.

General secretary Frances O’Grady said: “Companies like Sports Direct have put huge numbers of staff on zero-hours contracts, even as they expand and pay bonuses to senior staff.

“Employers like to argue that zero-hours contracts offer flexibility but for many they mean poverty pay and no way of knowing how often they’ll be working from one week to the next.”