A "staggering" 5.5 million workers could be on zero hours contracts, according to a study of 5,000 members of the Unite union.
A study found more than one in five Unite members were on zero hours contracts - five times higher than prior estimates - with half of respondents in the 16-30 category.
Unite general secretary Len McCluskey said the research suggests a "growing sub class" of insecure, low paid employment, with only one in seven wanting to remain on the contracts.
The results of the study by social survey company Mass1 came as employment rights will be debated on the first day of the TUC congress in Bournemouth today.
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