Collateral use of documents – what is it and what you need to know when disclosing documents

When parties are involved in court proceedings, they are often required to disclose documents that they would normally keep private and confidential. To encourage full and frank disclosure, the law generally protects those documents from being used for any other purpose outside the proceedings in which they were disclosed. This rule is embedded in CPR 31.22 and PD 57AD and is known in civil litigation as the “collateral undertaking”. 

This protection can be significant and what constitutes “use” of a document outside of the immediate proceedings is very broad. For example, the courts have held that documents disclosed in litigation cannot be used to put pressure on or threaten a third party outside the proceedings (see: Grosvenor Chemicals [2017] EWHC 1893 (Ch)). Doing anything other than realising, in the course of review for the purposes of the proceedings in which documents are disclosed, that a document would be relevant to contemplated other proceedings, may constitute collateral use (see: Tchenguiz v Grant Thornton [2017] EWHC 310 (Comm), [2017] 1 WLR 2908). 

However, the restriction is not absolute. In some circumstances, documents disclosed in one set of proceedings can be used for another purpose (for example, see CPR 31.22). This may be because the document has been referred to at a public hearing, the court grants permission, or the parties agree to its wider use. Knowing when these exceptions apply can be important, particularly in complex or high-profile disputes where documents disclosed in one case could have significant value in another. It is also worth remembering that parties, and in some cases third party owners of the documents, can ask the court to restrict or prevent a document from being used more widely, even if it has already been read by the court or referred to during a public hearing.

The boundaries of the court permission exception were recently explored in Hinduja v Hinduja & Anor [2026] EWCOP 34 (T3), where the court was asked whether documents filed in Court of Protection proceedings could be deployed in other proceedings. The decision in Hinduja serves as a reminder that permission to use documents for a different purpose is not granted lightly. Anyone seeking to do so must adopt a targeted approach whereby any application is made by reference to specific documents and to provide cogent and persuasive reasons for allowing the collateral use sought. The court must also be satisfied that there is no unwarranted prejudice to the disclosing party, and in doing so the court will undertake a balancing exercise. 

Against this background, there are two key points to keep in mind when disclosing documents:

• Think carefully about disclosure from the outset. If documents need to be disclosed, including before court proceedings have started, consider whether any additional undertakings are required from the recipient. This is particularly important if you are a third party who may have an interest in keeping the disclosed documents confidential or if documents are being disclosed as part of the pre-action stage procedure.
• Remember that disclosed documents cannot usually be used for any other purpose outside of the immediate proceedings. While there are exceptions, they are limited and parties should not assume that documents produced in one case can be freely used elsewhere.

For more information about the law, technology and practice of disclosure, contact Tom Whittaker or Stacie Bourton.