Friend or foe – common interest privilege between joint plaintiffs and joint defendants

Legal professional privilege (LPP) protects communications between a lawyer and a client if it was made for the dominant purpose of seeking or providing legal advice, or for use in anticipated legal proceedings.  When successfully claimed, LPP operates to keep the communication confidential.


If a communication subject to LPP is given to someone else, the privilege has been waived and is lost forever.  This is because the act of giving a privileged communication to a third party is contrary to any intention to keep it confidential.  There are exceptions to this, one being where the party entitled to claim privilege, and the person who is given the communication, have a recognised "common interest".  This can give rise to what is referred to as "common interest privilege".

Common interest privilege is not a free-standing form of privilege.  Rather, it is a defence to the argument that privilege has been waived by disclosing a privileged communication to somebody.  What relationships does common interest privilege protect?  The authorities have recognised the following as relationships which give rise to a commonality of interest:

  • insurer and their insured;
  • company and its director;
  • liquidator and their creditors;
  • parent company and wholly owned subsidiary; and
  • between co-defendants or co-plaintiffs (in some circumstances).

Friend or foe – commonality of interest between co-defendants

When determining whether common interest privilege exists between co-defendants, the motive of the parties can be relevant.  The Federal Court of Australia in Media Ocean Ltd v Optus Mobile Pty Ltd (No 10) [2010] FCA 1348 stated:

[T]wo persons interested in a particular question will not have a common interest for the purposes of common interest privilege if their individual interests in the question are selfish and potentially adverse to each other.  In such a case there will not be the necessary identity of interest.

The issue of adversity of interests is a key concern in determining whether common interest privilege arises between co-plaintiffs or co-defendants.  This is particularly the case where claims of accessorial liability are raised.  In such circumstances, can it be argued that co-plaintiffs/co-defendants have the requisite commonality of interest?  Or is the concept of accessorial liability such, that the parties interests will inherently be adverse to one another and/or selfish, to displace the commonality of interest?

Case law has indicated that the answer to the above lies in a contemporaneous analysis of the communication in question.  The key question is whether at the time the communication is made there is the requisite obligation of confidentiality.  The court should not find that the obligation of confidentiality is not present simply because there is a potential for the parties' relationship to change in the future: Cygnett v Souris [2020] FCA 1754 at [24].  That is, common interest privilege is not lost simply because it is possible to speculate that the interests of two co-defendants may diverge in the future.

Identifying common interest privilege – the takeaways

The line of authorities on the issue of common interest privilege has indicated:
  1. The key question is whether at the time the communication is made there is the requisite obligation of confidentiality either express or implied, such that a court should not refuse to imply the obligation of confidence on the basis that there is a potential for the parties' relationship to change in the future.
  2. It is not necessary for parties to share a common solicitor in order to claim common interest privilege so long as the communications are made to further the parties' shared interests.
  3. A common interest in the outcome of the litigation will generally be sufficient to allow a party to invoke common interest privilege.
McCabe Curwood is experienced in advising its clients on privilege and confidentiality issues.  Please contact us if you require advice on any matters covered by this article.

This article is not legal advice. It is intended to provide commentary and general information only. Access to this article does not entitle you to rely on it as legal advice. You should obtain formal legal advice that is specific to your particular circumstances.


Luke Dominish Associate
Samantha Beattie Lawyer