when I worked in the NHS, we had a small group of staff on zero hours contracts. They all had reasons why they didn't want to work set hours (one lived in Hong Kong and came home for the summer) In the NHS then, every time clinical staff started a new contract, they were required to do all the mandatory training and it took a while to get them onto the payroll, even if they were know to us and had worked with us recently. There was also the police check issue which again took time and cost us money. With a zero hours contract, they could contact us one day and start work the next. We kept records of their training so that they kept up to date and salary payment was not delayed.