You only have a clear right to a bonus if it is specified in your contract of employment. In such situations it may only apply if you attain specified targets, e.g. sell a certain number of products or increase your productivity by a certain amount.
However, if it has become custom and practice to pay one - in other words if you have automatically had one every year so far - you may be able to argue that it has become an unwritten part of your contract, and claim that an unlawful deduction has been made from your wages.
