As of 26 May 2015, any clause in a contract which stops a zero hour worker working for anyone else is unenforceable. This means workers are free to work for as many companies as they choose in order to work the number of hours that they want.
Although tackling zero hours contracts was a key plank of the Conservative manifesto, many have branded this new ban toothless as the new rules give employees no redress if the employer flouts the ban.
As well as this, some employers can try and get around this ban. For example by guaranteeing the worker one or two hours work a week so that it is not technically a zero hours contract.
However, it is a case of "watch this space" as the government does have the power to introduce anti-avoidance legislation to deal with these issues at a later date.