When you leave your place of work, you may be asked whether you want to sign a Settlement Agreement (formerly known as compromise agreements). Generally this will involve you agreeing not to take your former employer to Tribunal in return for a sum of money.
Before you do so you will need to talk to a qualified lawyer to explain what you are signing, otherwise the agreement will be null and void. Your employer will normally pay for this. I have extensive experience in providing such advice and will do so at a competitive fixed fee rate.