The Burger King judgement is relevant. If you are working a "Zero Hours Contract" and have to turn in for work without pay, then you have recourse to law. A ZHC is where your hours are not guarunteed. These are quite common, supply teachers are a case in point. An employer can no longer expect you to turn in and hang around on the offchance. Since 1995, you also have employment rights and benefit rights.
Google "zero hours contracts"