Privilege, Experts and the Boundary of Proper Defence Work

The governing principle is simple but demanding: protect candid legal analysis; preserve underlying evidence; investigate lawfully; and deploy material only after understanding what the step may expose or require next.

1. Begin with the item, not the label

“The file is privileged” is rarely a safe analysis. A file may contain legal advice, ordinary correspondence, pre-existing records, an expert’s calculations, client comments and copied documents. Different parts may have different status. The defence should identify the particular communication, document, data set, fact or object before deciding what protection applies.

2. Confidentiality and privilege perform different work

A solicitor must keep the affairs of current and former clients confidential unless disclosure is required or permitted by law or the client consents. That professional duty is broad. Legal professional privilege is narrower: where established, it is a substantive legal protection against compulsory disclosure. Confidential material is not automatically privileged, and privileged material should not be circulated merely because all recipients promise discretion.

3. Legal advice privilege

Legal advice privilege may protect confidential communications between lawyer and client made for the dominant purpose of giving or obtaining legal advice. Legal advice is not confined to a formal statement of law. It may include advice about what should prudently be done in the relevant legal context, including arrest, interview, search, bail, evidence, regulatory exposure and engagement with investigators.

The protection depends on the communication and its purpose. A fact does not become privileged because the client tells the solicitor about it. A pre-existing email does not become privileged because it is attached to a request for advice. The request and response may be protected; the underlying email remains what it was.

In an organisation, identify the client group authorised to seek and receive advice. Communications from employees outside that group may require separate analysis. Wide internal circulation can also weaken confidentiality and generate disputes about waiver or purpose.

4. Litigation privilege before charge

Litigation privilege may protect confidential communications with third parties and material created for the dominant purpose of conducting adversarial litigation that is in progress or reasonably contemplated. That can include appropriate expert work, witness material and forensic analysis. The protection is not triggered merely because a complaint has been made or because litigation is theoretically possible.

A focused criminal investigation, arrest, search or interview under caution may make prosecution sufficiently concrete, but the assessment remains fact-sensitive. Record what litigation was contemplated when the work was commissioned, why it was adversarial, and the dominant purpose of the communication or material. A later description cannot safely repair a purpose the contemporaneous evidence does not support.

5. Underlying evidence remains underlying evidence

Privilege protects qualifying communications and litigation work. It does not place a cloak over an object, independent record or pre-existing fact. Bank records, CCTV, messages, contracts, devices, photographs and physical items are not transformed merely because the lawyer or expert receives a copy.

• Preserve the original source and its provenance separately from legal annotations.
• Do not embed privileged comments into the only surviving copy of underlying evidence.
• Distinguish a lawyer’s selection or analysis from the source material selected or analysed.
• Assume investigators may lawfully obtain the same underlying material from its original controller.
• Do not move, alter, conceal or destroy material to improve its apparent legal status.

6. Physical evidence, wrongdoing and the point of refusal

The most difficult boundary arises when a client proposes destruction or concealment, reveals ongoing wrongdoing, provides a physical object or asks the lawyer to advance an account known to be false. Confidentiality does not authorise the solicitor to participate in obstruction, tamper with evidence or mislead investigators or a court.

The response is fact-specific. The lawyer should stop the proposed act, avoid taking steps that worsen the position, advise clearly on lawful conduct, preserve an accurate record and obtain immediate supervision or specialist professional-ethics advice where required. Continued acting may become impossible if the client insists that the lawyer mislead, conceal or facilitate criminal conduct. Withdrawal does not itself authorise disclosure; the disclosure question must be analysed separately.

7. Corporate investigations: decide who the lawyer acts for

An internal investigation may involve the company, directors, employees, insurers, regulators and external advisers. Their interests may overlap without being identical. At the outset, identify the client, who may instruct, who may receive advice, the purpose of each interview or report, and whether any individual requires separate representation.

• Do not promise an employee that the company’s privilege belongs to them.
• Explain the purpose of an interview and how the information may be used.
• Separate fact gathering, legal advice, disciplinary processes and regulatory reporting where their purposes differ.
• Limit circulation to those who need the material for the legal purpose.
• Reassess conflicts as evidence develops; apparent alignment at the start may disappear.
• Create separate factual communications where an insurer, employer or regulator needs information but not legal analysis.

8. Protecting privilege during searches and digital review

A device, mailbox or server may contain privileged communications among large volumes of ordinary material. The existence of privileged content does not necessarily prevent lawful seizure of the device or data source. It does require prompt, workable safeguards against review or use of protected material.

• Identify lawyer names, addresses, domains, matter references, date ranges and likely locations.
• Raise the concern as early and precisely as possible; a general assertion that “there will be legal advice” may not permit effective filtering.
• Seek segregation, independent filtering or an agreed review protocol appropriate to the power being used.
• Keep a schedule of disputed material and the basis of each claim.
• Preserve enough information to challenge an erroneous determination without disclosing more advice than necessary.
• Escalate urgently if privileged material appears to have reached the investigative team.

9. Experts begin with a question, not a desired answer

An expert is needed when a defined issue requires specialist knowledge. The seriousness of the allegation does not itself justify expert evidence, and an instruction framed as “find support for the client” compromises the work before it begins. The expert must be given a neutral question, a balanced evidential foundation and permission to identify limitations and adverse matters.

10. The expert’s independence starts before any report

If expert evidence is later used in criminal proceedings, the expert’s duty is to help the court by objective and unbiased opinion within their expertise. That duty overrides loyalty to the party paying the fee. Good instructions therefore identify the issue and relevant assumptions without dictating the conclusion.

• Select the discipline and expert for the actual question, not reputation alone.
• Check competence, experience, accreditation, conflicts and material adverse professional history.
• Provide relevant favourable and unfavourable material, with a clear source schedule.
• Distinguish facts, disputed propositions, instructions and assumptions.
• Ask the expert to identify missing data, alternative interpretations and limits of confidence.
• Keep a record of substantive oral discussions and changes to the question or material.
• Never ask the expert to omit a qualification or alter an opinion for tactical convenience.

11. Drafts, adverse opinions and second experts

An unfavourable opinion is not a failed instruction. It may show that the proposed defence theory is wrong, the data are inadequate, the question belongs to another discipline or a damaging risk must be managed. Clarification is legitimate. Pressure for a preferred conclusion is not.

A genuine second opinion may be proper where the first expert lacked the correct discipline, worked from incomplete material, used a disputed method or left a material issue unresolved. The reason should be recorded. A later expert must not be given a selectively improved evidential foundation that hides relevant facts or earlier technical work.

A confidential unused defence report will often remain privileged. There is no safe universal rule that every abandoned report must be handed to the prosecution. Equally, privilege does not erase separate procedural obligations. After a defence statement, section 6C may require notice identifying an expert instructed to provide an opinion, whether or not that opinion is ultimately relied upon. If expert evidence is introduced, Part 19 governs the expert’s duty, the report and access to examinations, tests and underlying material. Advice must therefore be taken before changing experts, serving a report or assuming that unused work is consequence-free.

12. Deployment changes the analysis

The decision to disclose an expert report or other protected analysis should be directed to a defined investigation or charging decision. Once material is deployed, the defence may waive privilege in it and create arguments about the associated instructions, assumptions, data, records or communications necessary to understand it fairly. The scope of any waiver is fact-sensitive and should not be guessed after disclosure has occurred.

• What precise decision is the material intended to influence?
• Can verified underlying facts achieve the objective without disclosing legal analysis?
• Is the document final, accurate and based on a complete evidential foundation?
• What material is incorporated, summarised or necessary to understand the conclusion?
• What adverse qualification or alternative opinion must be addressed?
• Who should receive it, on what stated basis, and can disclosure realistically be limited?
• What procedural or professional step will follow if the material is later relied upon?

13. Sharing information outside the legal team

Employers, regulators, insurers, banks and family lawyers may have a legitimate need for information. Forwarding legal advice wholesale is rarely the only response. A separate factual notice or authorised summary can often satisfy the external purpose while protecting the reasoning, uncertainties and strategy within the legal advice.

Before sharing, identify the recipient’s legal basis, the minimum information required, whether the account is consistent but appropriately tailored to that process, and whether disclosure may waive privilege or create a new evidential record. “Without prejudice” and “confidential” headings do not solve those questions.

14. Two practical examples

Example one: the copied mailbox

Investigators proposed to examine a senior manager’s mailbox after seizure of company systems. The mailbox contained years of ordinary business material and a concentrated period of communications with external lawyers. The defence did not rely on a general assertion of privilege. It identified the legal team, domains, matter names and date ranges, proposed segregation and kept a schedule of disputed items. The safeguard was workable because the claim was specific enough to test without opening the advice to the investigative team.

Example two: the first expert did not support the theory

A technical expert concluded that the available data could not support the client’s preferred explanation. The defence tested whether the expert had the correct data and discipline, then recorded the limits of the opinion. A second specialist was instructed only on a distinct issue the first expert had identified as outside their expertise. The later instruction included the adverse data and the first expert’s relevant technical work. The strategy changed because the evidence changed; the experts were not asked to change the evidence.

15. The boundary review

• Identify: What exactly is the item, communication, fact, object or expert product?
• Classify: Is it confidential only, privileged, underlying evidence, or mixed?
• Protect: Who needs access, and what segregation or circulation limit is required?
• Test: Can the claimed purpose, confidentiality and contemplated litigation be evidenced?
• Use: What defined decision would retention, limited disclosure or deployment improve?
• Consequences: What waiver, service, expert, ethical or professional obligation may follow?
• Review: What has changed, and what must now be reclassified, protected, disclosed or left alone?

The result should be an auditable decision, not a reflex. The defence should be able to explain why material was protected, why an expert was instructed, why an opinion was or was not used, and how the underlying evidence remained intact.

Legal source note

This chapter draws on the Criminal Procedure Rules 2025, Part 19; section 6C of the Criminal Procedure and Investigations Act 1996; sections 10 and 11 of the Police and Criminal Evidence Act 1984; the current SRA Code of Conduct for Solicitors (including paragraphs 1.4, 2.1–2.4 and 6.3); and the modern appellate treatment of legal advice and litigation privilege, including Three Rivers (No 6), SFO v ENRC and R (Jet2.com) v CAA. Those authorities are necessarily summarised for a public guide. Privilege and professional-conduct decisions are fact-sensitive and require case-specific advice.

Primary and official sources are listed in the guide-wide source register.