How to Handle a Disciplinary Investigation UK: The Process That Determines Whether You Win at Tribunal
A fair investigation is the foundation of every lawful dismissal. Skipping it or rushing it is the most common reason employment tribunals find dismissals unfair. Here is how to run one properly.
Leon Mclean
Co-founder, Birchlow · Last reviewed June 2026
The investigation is not the same as the disciplinary hearing
Many employers conflate the investigation meeting with the disciplinary hearing. They are separate stages with different purposes. The investigation gathers facts. The hearing decides whether those facts amount to misconduct and what sanction, if any, is appropriate. Mixing the two, for example telling an employee in the investigation meeting that they are dismissed, is a fundamental procedural error that will be difficult to defend at tribunal regardless of the underlying conduct.
Employment tribunals do not just ask whether the employee did what the employer says they did. They ask whether the employer found that out properly. The test set out in British Home Stores v Burchell, still applied by tribunals today, requires the employer to show three things: genuine belief that the employee was guilty, reasonable grounds for that belief, and a reasonable investigation that produced those grounds. The investigation is the step most often skipped or rushed, and it is the step that most often causes an otherwise defensible dismissal to fail.
Why the investigation determines everything
An employer who dismisses without investigating, or who investigates superficially, cannot demonstrate the second and third elements of the Burchell test. A tribunal does not require the employer to have conducted an exhaustive investigation. It requires a reasonable one. What is reasonable depends on the circumstances: a more serious allegation warrants a more thorough investigation.
The ACAS Code of Practice on Disciplinary and Grievance Procedures requires employers to carry out a thorough investigation of the relevant facts before taking formal disciplinary action. The Code also requires the investigation to be carried out without unreasonable delay. Delay that disadvantages the employee, for example because witnesses' memories have faded or evidence has been lost, is itself a procedural defect.
The practical consequence is straightforward. An employer who dismisses on genuine grounds but without a documented investigation is likely to lose at tribunal. The employee's conduct may not be in doubt. The employer's process is.
When to suspend and when to investigate
In serious cases, the employer may need to suspend the employee on full pay while the investigation takes place. Suspension is appropriate where:
- →the employee's presence at work might compromise the investigation by influencing witnesses or accessing relevant evidence
- →the alleged conduct is so serious that the employee's continued presence would be untenable
- →there are safety concerns about the employee being on site
Suspension should be set out in writing, described as precautionary and not as a disciplinary measure, and confirmed to be on full pay. Suspending without pay creates a separate claim for unlawful deduction from wages. Suspending in all disciplinary cases as a matter of routine, without considering whether it is necessary, is something tribunals and ACAS guidance both criticise.
How to run the investigation properly
Appoint an appropriate investigator. The investigator should be someone who was not directly involved in the alleged incident. They should not be the person who will chair the disciplinary hearing. Where possible, they should have no strong pre-existing view about the employee. In a small business, this may mean asking a senior manager from a different department, or taking professional HR support for the investigation.
Identify what you need to find out. Before conducting any interviews, list the key factual questions the investigation needs to answer. What is alleged to have happened? When? Where? Who was present? Are there documents, records or CCTV footage relevant to the allegation? What does your disciplinary policy say about this type of conduct?
Interview the relevant people. Speak to the employee under investigation and to any witnesses. Keep a note of every interview: the date, who was present, and what was said. Do not record interviews without consent. Do not coach witnesses or suggest the answers you expect to hear. Ask open questions and let the interviewee respond.
Invite the employee to an investigation meeting. The employee under investigation should be invited to an investigation meeting to give their account. Tell them the nature of the allegation before the meeting so they can prepare. A worker can request to be accompanied to an investigation meeting if it may lead to formal action, though the statutory right to be accompanied applies to formal disciplinary hearings rather than investigation meetings. Good practice is to allow a companion.
Gather and retain documentary evidence. Collect and preserve any relevant documents before the investigation is complete: CCTV footage that may be overwritten, emails, timesheets, attendance records, previous warnings and any other records relevant to the allegation.
Be thorough but proportionate. A minor conduct matter does not require weeks of investigation. A serious allegation involving potential gross misconduct does. Match the depth of the investigation to the seriousness of the matter. An investigation that is too brief will not withstand tribunal scrutiny. An investigation that is disproportionately prolonged causes its own problems, particularly if the employee is on suspension.
How to document the investigation
Write an investigation report. At the conclusion of the investigation, the investigator should produce a written report setting out the facts established, the evidence gathered, the questions that remain unresolved and a recommendation on whether there is a case to answer. The report should not state a conclusion on guilt or recommend a sanction. Those are for the hearing chair.
Share the report before the hearing. The employee must be given a copy of the investigation report, and any documents relied upon, before the disciplinary hearing. Giving the employee inadequate notice or withholding relevant documents until the hearing itself is a procedural defect. The employee needs time to consider the evidence and prepare their response.
Retain all documentation. Keep the investigation notes, the report and the supporting evidence. If the case ends in dismissal and the employee brings a tribunal claim, this documentation is your primary defence. Losing or failing to retain it puts you in a very difficult position.
How the investigation connects to the hearing
The disciplinary hearing chair should receive the investigation report before the hearing and should not be the person who conducted the investigation. At the hearing, the chair presents the allegations and the evidence, the employee responds, and the chair adjourns to consider the decision. The hearing chair's decision must be based on the evidence established in the investigation. Introducing new evidence at the hearing that was not shared with the employee in advance is a procedural defect.
Where the hearing reveals that the investigation was incomplete, the chair should adjourn and ask the investigator to carry out further investigation before reconvening. Pressing ahead with an incomplete investigation because the employer wants to reach a conclusion quickly is one of the most common and costly mistakes in disciplinary proceedings.
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