“Without prejudice” is a phrase that appears constantly in dispute resolution — on letters, in mediation agreements, in court judgments. Most people have a vague sense that it means something cannot be used against them. That is broadly right, but the detail matters, particularly in the context of mediation.
What “without prejudice” means
The without prejudice rule is a rule of evidence. It provides that communications made in a genuine attempt to settle a dispute cannot be used as evidence in court proceedings. The rationale is straightforward: if parties know that offers and concessions made in settlement negotiations can be used against them at trial, they will be reluctant to negotiate frankly. The rule removes that inhibition.
For a communication to be protected, two conditions must be met. First, there must be an existing dispute between the parties. Second, the communication must be a genuine attempt to settle that dispute. A letter that is headed “without prejudice” but which is not genuinely aimed at settlement may not be protected — the label does not automatically create the protection.
Communications that are protected cannot normally be referred to in court, whether to prove what was said, to establish an admission, or to show that an offer was made or rejected. The rule applies whether the communication is in writing or oral.
How the rule applies in mediation
Mediation takes place entirely on a without prejudice basis. This is fundamental to the process.
Everything said during the mediation — in the joint session and in private caucuses — is without prejudice. Offers made, positions explored, admissions made in the course of negotiation, concessions floated and then withdrawn — none of these can be referred to in subsequent court proceedings. The parties sign a mediation agreement before the day begins which makes this explicit.
This confidentiality is what makes frank discussion possible. A party can explore a settlement figure lower than they would accept without that number being used against them. They can acknowledge a weakness in their case without that acknowledgement being put to them under cross-examination. They can discuss interests and concerns that go beyond their legal position without fear of prejudicing their case.
The without prejudice rule and the mediator
The mediator is also bound by confidentiality. A mediator cannot be called as a witness in subsequent proceedings to give evidence about what was said during the mediation. This protection is essential — without it, parties would not be able to speak candidly in private sessions, and the process would be undermined.
What the mediator learns in private sessions is confidential not only from the court but from the other party. I will not share what you tell me with the other side without your express permission. This is a separate layer of confidentiality on top of the without prejudice protection.
”Without prejudice save as to costs”
There is an important qualification to the without prejudice rule. A communication marked “without prejudice save as to costs” (sometimes called a Calderbank offer, or more commonly today a Part 36 offer) is protected from disclosure during the trial on the merits, but can be shown to the court when it comes to deciding who pays the costs.
This matters in mediation because, if a party makes a genuine offer to settle during the mediation that the other side unreasonably refuses, that refusal — and the offer — may be relevant to a later costs application if the case proceeds to judgment. The without prejudice protection does not prevent the court from considering whether a party acted reasonably in relation to settlement.
What happens if someone tries to use mediation communications in court?
If a party attempts to refer to communications made in the mediation in subsequent proceedings, the other party can apply to have them excluded. Courts treat such attempts seriously. The without prejudice rule is a substantive protection, and breaches of it — whether by disclosing what was said in a mediation or by attempting to use a without prejudice document in evidence — are not taken lightly.
The practical implication
The without prejudice nature of mediation is one of its most significant advantages over litigation. It creates a protected space in which both parties can explore settlement options that would be too risky to raise in open correspondence. A party who understands this — and uses it — is in a much stronger position to reach a resolution that works for them.
If you have questions about how the without prejudice rule applies to your specific situation, your solicitor is the right person to advise you. But as a general principle: in mediation, what is said in the room stays in the room.