There are a number of well-known principles that place restrictions upon the use and disclosure of documents in a legal proceeding. Documents subject to legal professional privilege is one example.
A lesser known rule, which can have very real practical consequences for all parties and interested persons in litigation, is the “Harman rule”. The rule provides that where a party has been compelled to disclose a document or information in the course of legal proceedings, another party cannot use this material for any purpose other than for which it was given.
As the compulsory nature of court proceedings violates a party’s privacy and right to confidentiality, the rationale behind the Harman rule is to prevent the further use of this material for other purposes which would be unfair in the circumstances.
Broad obligation and wide application
The rule imposes a very broad obligation. Not only does it apply to parties to a legal proceeding, it also binds third parties and any other persons involved in litigation, including officers or agents of a litigant, a litigant’s solicitor, and both lay and expert witnesses.
The application of the rule is also wide and applies to any information contained in documents that have been disclosed, including: documents inspected in the discovery process, affidavits, answers to interrogatories, documents produced by subpoena, expert reports, and witness statements.
This information is to remain strictly confidential between all involved parties until the time the information is read in open court, which will usually occur during the final hearing of the matter. It is only at this point in time that parties will be released of their obligations under the Harman rule.
It is also important to bear in mind that the undertaking extends not only to court proceedings, but may also apply to information disclosed through arbitration and mediation processes and in some tribunals.
A practical example of the rule’s operation
If an affidavit that has been served on a party, but not yet tendered in court, discloses certain information that could be used for business purposes, the other party must keep this material strictly confidential until it becomes part of the public record. Using this information to gain a competitive advantage over the other party prior to this would constitute a breach of the Harman rule.
Consequences: contempt of court
The Harman rule is an implied undertaking and is an obligation owed not to the other party but to the court. As such, any person or party breaching this undertaking risks being held in contempt of court.
Whilst the Harman rule may prove frustrating for some parties to a legal proceeding, it is important to bear in mind that this implied undertaking is the condition upon which documents are made available to a parties to a legal proceeding. Despite that certain material may be in a party’s possession, there is no right to use this information for a purpose other than for the particular legal proceeding in question.
Given that the misuse of documents in breach of this undertaking may be construed as contempt, all persons involved in litigation should be aware of the importance of keeping discovered information secure and the limitation placed on its use when leave of the court has not been obtained.
 Adopted by the High Court of Australia in Hearne v Street  HCA 36. The undertaking stems from the case Harman v Secretary of State for the Home Department  1 AC 280.