The "implied undertaking" and Discovery (Disclosure)
of documents in UK Law:

In Halsbury's Laws of England, 4 Edition, paragraph 66, dealing with the use of documents disclosed on discovery, it is stated:

 THERE is an implied undertaking by the party on whom a list or affidavit of documents is served or to whom the documents are produced that he will not use them or any information obtained from them for a collateral or ulterior purpose; an improper use of the documents amounts to a contempt of court."

In a footnote to the text Halsbury goes on to state that

  such an undertaking is also binding on anyone into whose hands the documents may come if he knows that they had been obtained by way of discovery"

and cites the decision in Distillers Company (Biochemicals) Limited v Times Newspapers Limited [1975] 1 All ER 41. Mr Stephens on behalf of the plaintiff submits that if the "original documents" were the source of the article in the Phoenix, as the plaintiff alleges, the defendants must have known that they were documents disclosed on discovery in the course of earlier litigation and that the defendants were bound by the implied undertaking not to use them or any information obtained from them for a collateral or ulterior purpose. In that case Talbot J in the course of his judgment stated at page 48F:

  The plaintiffs claim an overriding protection from publication and use of their documents which they were compelled to disclose in the action against them. They claim this protection involves those in whose hands the documents come, particularly where the possession was unlawfully obtained. I do not doubt the correctness of this proposition; I do not think that on the authorities and for the proper administration of justice it can be argued to the contrary. Those who disclose documents on discovery are entitled to the protection of the court against any use of the documents otherwise than in the action in which they are disclosed. I also consider that this protection can be extended to prevent the use of the documents by any person in whose hands they come unless it be directly connected with the action in which they are produced. I am further of the opinion that it is a matter of importance to the public, and therefore of public interest, that documents disclosed on discovery should not be permitted to be put to improper use and that the court should give its protection in the right case.

quoting Haughey v Prendiville and Penfield Enterprises Ltd, Chancery Division, SWEC 2228, (Transcript).