A breach of contract can be very serious. It could result in you being unfairly or wrongfully dismissed, having unlawful deductions made from your wages or changes to your entitlements to name a few.
If you think there has been a breach of contract by you or your employer you should first try to resolve this with them directly. Remember, they have a duty to provide a grievance procedure. Make use of it. It will help you later if you end up at an Employment Tribunal. It will also help you keep within the time deadlines.
In most cases, you must make your application to an employment tribunal within three months minus one day of the date when the event you are complaining about last happened.