A many as 5.5 million workers in Britain could be signed up to zero - hour contracts, a new research shows.According to a study of 5,000 members of Britain's largest trade union, Unite, more than one fifth (22%) of workers employed by private businesses were on zero-hour contracts, five times higher than previous estimates. The study by the social survey company Mass1 also suggested that people aged under 30 are more likely to be on a zero-hour contract. Under the contract, workers are not guaranteed work from one week to the next and they must be ready to work whenever they are asked instead of working a specific number of hours per week. Unite said the findings showed that employers were “exploiting” the contract to avoid paying holiday pay and sick pay. “An economy built on the back of insecure work and exploitation will not deliver a sustainable recovery. We need urgent action to end the growth of this pernicious form of employment and to end this government's never-ending attacks on workers' rights,” said Unite general secretary Len McCluskey. Earlier in August, it was found that over one in four companies in Britain have staff on controversial zero-hour contracts. According to a study by the Recruitment and Employment Confederation among 600 employers, some 27 percent used zero-hours contracts.