When you leave a job it’s either because you want to, or you have to because of a personal reason, or it’s because your employer no longer wants you to remain!
If you leave at your own volition you will be contractually bound to work your period of notice, as per your contract of employment. It may be that this period of notice is waived by mutual consent but it cannot be waived unilaterally by either party. Your contract may restrict your choice of future employer if it contains any restrictions – this will be to protect your present employer‘s future trade with his existing client base. However, such clauses, known as restrictive covenants are sometimes held to be unreasonable and thus non-enforceable.
If your employer dismisses you he must do so after following correct procedures, giving you due notice and paying you a redundancy payment (minimum amount payable is set out by law) if your employment exceeds one calendar year. If, however, the reason for your dismissal is incompetence, incapacity or gross breach of contract, no such redundancy is payable.