John Hannett of Usdaw said “millions” of workers were being exploited because of the government’s ideological fixation on the free market.

And Ronnie Draper of the Bakers, Food and Allied Workers union noted that Labour proposals to allow workers to request regular hours after 12 months were “a load of rubbish.

“What if they don’t get 12 months, or six months? What if they are let go after five and a half?” he asked.

Delegates slammed contracts that deprive employees of any ability to plan their lives.

Unite assistant general secretary Diana Holland spoke of a mother who was told at 4am she would be expected at work at 5 and needed to find a way for her child to get to school.

Whatever such contracts were labelled “they are all about the same thing — giving employers power. The power to control lives,” she said.