In most cases, the Employment Tribunal imposes a three month time limit on issuing Employment Tribunal proceedings relating to a complaint. If you are dismissed, this generally means three months from the date of dismissal. If you have become the subject of discrimination, this is 3 months from the date that the discrimination occurred.
Whilst the tribunal does have some latitude in extending the time limits, this will only be done in limited circumstances. It is therefore imperative that legal advice is obtained at the earliest possible opportunity.