One powerful type of evidence, which is also very rare, is witness evidence.Obviously it’s a risky business being a witness for a colleague against your employer, and for this reason it is unusual to have any witnesses at all. If you are lucky enough to have a witness at work willing to stand up for you, then you may be surprised to learn that this is not always helpful during a negotiation for a couple of reasons:
 An employer will usually want a settlement agreement to be confidential. This includes the facts of the allegations you intend to make being kept confidential from other employees. If you ask other employees to be witnesses then you will necessarily disclose facts of your case to them, making the employer less likely to agree to a settlement agreement.
 Witnesses are only useful to support disputed allegations. Often in employment negotiations, if allegations are disputed then they usually remain disputed, but the parties agree to disagree and settle. If witness evidence, such as a witness statement, is produced, the employer is likely to instruct lawyers and start to defend the allegations, which is not what you want to happen.
When witnesses are most valuable
If, however, you have been subject to discrimination or harassment and the only way you can make your case to your employer is by using witness evidence, then you may want to ask a colleagues to provide evidence in support of your claims. Be aware though that your colleagues won’t necessarily want to get involved. They may not be willing to expose themselves to the same problems you have suffered, or they may simply disagree with you.
It’s very common at employment tribunals for the claimant to be the only witness because no one in the company will come forward to support them. So don’t be surprised if you approach a colleague to be a witness and he or she is reticent or simply refuses.
What form should witness evidence take?
If you are going to approach witnesses, the best approach is to ask them to make a written witness statement and then to sign and date it there and then, while they still feel inclined to do so. Alternatively, if you raise a grievance, you could ask the company to interview witnesses for you, although this may well let the employer persuade the witnesses into giving evidence favorable to them and not you.