Legal Professional Privilege in Practice: A Guide for Solicitors

Legal professional privilege is one of the oldest and most fiercely protected doctrines in English law, and one of the easiest to lose through a careless email, a copied-in third party, or a poorly scoped internal investigation. Every solicitor understands the basic idea — that communications with a client for the purpose of giving or receiving legal advice are protected from disclosure — but the practical edges of the doctrine, where it is tested and sometimes lost, are less well understood. This guide sets out the two branches of privilege, the leading authorities that define their limits, and the everyday pitfalls that put privilege at risk, alongside relevant CPD courses for legal professionals covering privilege and professional conduct.

The Two Branches of Privilege

English law recognises two distinct forms of legal professional privilege, and confusing them is a common source of error. Legal advice privilege protects confidential communications between a lawyer and client made for the dominant purpose of giving or seeking legal advice, whether or not litigation is in prospect. Litigation privilege is broader in one sense and narrower in another: it protects confidential communications between a lawyer or client and a third party, made for the dominant purpose of litigation that is pending, reasonably contemplated, or actually underway — but unlike legal advice privilege, it requires litigation to be in contemplation at all.

The distinction matters most when a third party is involved. Legal advice privilege, as confirmed in the landmark case Three Rivers District Council v Governor and Company of the Bank of England (No 5) [2003] EWCA Civ 474, applies only to communications between the lawyer and the client — and the Court of Appeal in that case took a narrow view of who counts as "the client" within a large organisation, limiting it to those specifically tasked with seeking and receiving legal advice on the client's behalf. Litigation privilege, by contrast, can extend to communications with third parties (such as expert witnesses or investigators) provided the dominant purpose test is met.

The Dominant Purpose Test

Both branches of privilege turn on the same core question: what was the dominant purpose of the communication? A document created for several reasons — partly for legal advice, partly for a commercial or administrative reason — is only privileged if the legal purpose was the dominant one, not merely a purpose among several. This was reaffirmed decisively by the Court of Appeal in Director of the Serious Fraud Office v Eurasian Natural Resources Corporation Ltd [2018] EWCA Civ 2006, a case that significantly widened the practical availability of litigation privilege for companies facing the prospect of a criminal or regulatory investigation.

In SFO v ENRC, the Court of Appeal held that litigation privilege could attach to documents created during an internal investigation once a company reasonably contemplated a criminal prosecution — even before the SFO had confirmed it was formally investigating — and that this included interview notes and other investigative materials created for the dominant purpose of resisting or responding to that anticipated litigation. The judgment corrected what had been seen as an overly restrictive first-instance decision, and is now the leading authority firms rely on when structuring internal investigations to preserve privilege from the outset.

Waiver: How Privilege Is Lost

Privilege belongs to the client, and only the client can waive it — but waiver can happen inadvertently, and once it happens it is very difficult to reverse. The core principles are well established through a body of case law including Balabel v Air India [1988] Ch 317, which confirmed that privilege covers the whole continuum of communications between lawyer and client relating to the transaction in which advice is sought, not just documents that contain advice in explicit terms, and Waugh v British Railways Board [1980] AC 521, the House of Lords decision that first firmly established the dominant purpose test for litigation privilege.

Waiver typically occurs in a handful of recurring ways:

• Voluntary disclosure. Sharing a privileged document with an opposing party, or referring to its contents in open correspondence, will usually waive privilege in that document — and can waive privilege in related documents on the same issue ("collateral waiver").
• Disclosure to third parties without a common interest. Copying in someone outside the privileged relationship — a commercial partner, an unrelated group company, or a regulator — without a recognised common interest can waive privilege in that communication.
• Deploying privileged material in litigation. Relying on part of a privileged document to support your case, while withholding the rest, is a well-recognised route to a court ordering wider disclosure.
• Mistake and inadvertent disclosure. Accidentally including a privileged document in a disclosure bundle does not always waive privilege — courts have granted relief where it is obvious the mistake occurred — but relying on that safety net is risky, and the receiving solicitor's own professional obligations on inadvertent disclosure come into play too.

Common Pitfalls in Everyday Practice

Most privilege disputes do not arise from dramatic courtroom tactics — they arise from ordinary working habits that quietly erode the protection. The recurring pitfalls include:

Privilege and Third-Party Tools: A Modern Risk

Privilege depends on confidentiality being maintained throughout — which means how a firm handles client information digitally is now directly relevant to whether privilege survives. Pasting privileged material into a public AI tool without checking its data-handling terms, or routing sensitive documents through unapproved cloud services, can undermine the confidentiality that privilege depends on before a dispute ever reaches a court. This is a growing area of practical risk; our companion guide on AI-assisted drafting and document review sets out the confidentiality and privilege risks of AI tools in more detail, and the supervision and verification standards the SRA expects firms to apply.

Structuring Internal Investigations to Preserve Privilege

Given the SFO v ENRC guidance, firms conducting or advising on internal investigations should take deliberate steps from the outset rather than trying to reconstruct privilege after the fact:

• Document, contemporaneously, the point at which litigation or a regulatory investigation was reasonably contemplated — this evidentiary record matters if privilege is later challenged.
• Instruct external or in-house lawyers to lead the investigation, and make clear in engagement terms that its dominant purpose is anticipated legal proceedings, not general fact-finding or business as usual.
• Keep witness interview notes and investigation working papers distinct from any parallel commercial or HR process, so the dominant purpose of each document set is clear.
• Limit circulation of investigation materials strictly to those who need them for the legal purpose, applying the same discipline as with any other privileged communication.

FAQ

What is the difference between legal advice privilege and litigation privilege?

Legal advice privilege protects lawyer-client communications for the dominant purpose of giving or seeking legal advice, with no need for litigation to be contemplated. Litigation privilege protects communications with lawyers or third parties made for the dominant purpose of litigation that is pending, reasonably contemplated, or underway.

Can privilege be waived by accident?

Yes — inadvertent disclosure, careless copying of third parties, or deploying part of a privileged document in argument can all risk waiver, even without any intention to give up the protection. Courts have some flexibility to grant relief for obvious mistakes, but it is not guaranteed.

Does privilege automatically apply to internal investigation documents?

No. Following SFO v ENRC, an internal investigation attracts litigation privilege only where litigation was reasonably in contemplation and the dominant purpose of the specific document was that anticipated litigation — not simply because an investigation is happening.

Who owns privilege — the lawyer or the client?

The client. A lawyer cannot waive privilege on their own initiative; only the client can authorise disclosure of privileged material, and lawyers should advise clients clearly before any step that risks waiver.

Legal professional privilege rewards careful, deliberate practice — in how documents are created, who is copied in, and how investigations are structured from day one. Getting the dominant purpose test and waiver risk right is core professional knowledge that every solicitor needs to keep current as the case law develops. Learnsignal's CPD courses for legal professionals cover privilege, professional conduct, and the practical compliance skills firms need — browse the current programme to keep your practising certificate requirements on track.