Any entitlement you may have to bonus payments depends on whether there is an agreement between you and your employer. If there is a contractual right to a bonus (i.e. there is an express term or implied term in the contract of employment, or an implied term, e.g. custom and practice), then failure to pay the bonus would be a breach of contract.
If it is clear that the employer has discretion over whether to pay a bonus or not, there is unlikely to be a contractual entitlement. Even so, it has been held that, even where the employer has stated bonus payments are discretionary, because the parties intended the bonus would be paid in all but extraordinary circumstances, a bonus payment was due.
Even if a bonus is discretionary, your employer must act rationally and not arbitrarily when deciding whether to pay you a bonus and how much. And your employer must not discriminate unlawfully, for example by paying higher bonuses to men than women, or victimise you, for example, withholding your bonus because you have blown the whistle about unlawful activity where you work.