The number of workers on zero-hours contracts has increased by almost a fifth to 744,000, new figures show. 
People on a zero hours contract in their main job represented 2.4 per cent of all those in employment in April-June, compared with the same period a year ago, the Office for National 
Statistics says. 
The new figure will fuel fresh controversy over the use of the contracts, under which employees do not know how much work they have from one week to the next. 
Research published by the TUC shows average weekly earnings for zero-hours workers are £188, compared to £479 for permanent workers. 
Two-fifths of zero-hours workers earn less than £111 a week – the qualifying threshold for statutory sick pay – compared to one in 12 permanent employees. 
TUC general secretary Frances O'Grady said: “Zero hours contracts are a stark reminder of Britain’s two-tier workforce. 
“People earn £300 a week less, on average, than workers in secure jobs. 
A Business Department spokesman said: “Zero hours contracts have a part to play in a modern, flexible labour market. 
“For workers such as students and those with caring responsibilities they provide a pathway to employment, particularly when the individual cannot commit to regular hours. 
“However we have acted to ban the use of exclusivity clauses in these contracts which prevent people from boosting their income when they have no guarantee of work.”