Mediator in the witness box?

One of the many reasons for disputing parties to attempt mediation as a method of resolving their quarrel is the confidentiality that covers the process. This is usually enshrined in the mediation agreement.
However, Farm Assist v Secretary of State for the Environment, Food and Rural Affairs [2009] All ER (D) 228 (Jun) shows that the court will always consider the interests of justice above any agreements reached by the parties on confidentiality; the agreement will only form a part of the court’s decision.

Facts of the case

Farm Assist (FAL) was seeking to set aside a settlement agreement entered into following a mediation with Defra, on the grounds of economic duress.
The mediation took place in 2003. The mediator and the parties had entered into a mediation agreement containing the usual provisions about confidentiality. Specifically (in summary); All communications were to be without privilege; None of the parties would call the Mediator as witness in any litigation/arbitration