When a serious workplace matter arises — an allegation of misconduct, a harassment complaint, a potential gross misconduct situation — the quality of the investigation that follows will determine everything. A thorough, fair, and well-documented investigation provides the foundation for a defensible outcome. A rushed, biased, or poorly recorded investigation is often where the legal case against the employer is built.
Running a fair workplace investigation is not about finding the outcome you want. It is about following a process that reaches the right conclusion — and doing so in a way that would withstand scrutiny from an employment tribunal if challenged. This guide explains what that process looks like in practice.
When Is a Formal Investigation Required?
Not every workplace matter requires a formal investigation. Minor conduct issues can often be addressed through an informal conversation. A formal investigation is needed when: a formal grievance has been raised; the conduct alleged is serious enough that it might result in a formal disciplinary sanction; there are conflicting accounts that need to be assessed; or the matter involves allegations of bullying, harassment, or discrimination.
The decision about whether to investigate, and at what level, should be made by HR or a senior manager with access to HR guidance — not by the line manager closest to the situation.
The Investigator: Independence Is Essential
The person conducting the investigation must be genuinely independent of the matter being investigated. They should not have a pre-existing view of the outcome, should not be a close colleague of either the complainant or the respondent, and ideally should not be the person who will conduct any subsequent disciplinary hearing. This separation — between investigator and decision-maker — is a basic requirement of a fair process under the ACAS Code of Practice.
For small businesses, achieving this independence can be challenging, particularly where the matter involves senior staff or where the management structure is flat. In these situations, bringing in an external HR consultant to conduct the investigation is often the most practical solution.
Suspension: Use Sparingly and With Justification
Where allegations are serious, employers sometimes consider suspending the employee under investigation. Suspension should not be a default response — it should only be used where there is a genuine need: for example, where the employee’s presence in the workplace risks evidence being compromised, witnesses being pressured, or other staff being put at risk.
Suspension must be on full pay unless the employment contract specifically provides otherwise. An unjustified or disproportionate suspension can itself give rise to a constructive dismissal claim, so the decision should always be documented with clear reasoning.
The Investigation Process Step by Step
Step 1: Define the Scope
Before interviewing anyone, clearly define what the investigation is looking at. What specific allegations or matters are in scope? This prevents the investigation from drifting, keeps it proportionate, and ensures the subject of the investigation knows what they are facing.
Step 2: Gather Documents and Evidence
Identify and preserve any documents, messages, records, or other evidence relevant to the allegations. This includes emails, attendance records, CCTV footage, written statements, or any other material that could assist in establishing the facts.
Step 3: Interview Witnesses
Interview witnesses individually, in private, and without the presence of others from the same team where possible. Use open questions — not leading questions that suggest a particular answer. Take a detailed contemporaneous note of each interview, and ideally have the witness review and sign the note to confirm its accuracy.
The subject of the investigation should always be given the opportunity to give their account — this is a fundamental requirement of a fair process. They have the right to be accompanied by a trade union representative or colleague at any formal interview stage.
Step 4: Assess the Evidence
Once all evidence has been gathered, assess it objectively. Where accounts conflict, weigh the evidence on the balance of probabilities — which version of events is more likely to be true, based on the totality of what you have found? Document your reasoning clearly. Note what evidence you found credible and why.
Step 5: Write the Investigation Report
Produce a written investigation report that sets out the allegations, the evidence gathered, the assessment of that evidence, and conclusions on the facts. The report should not reach a decision on any disciplinary outcome — that is for the disciplinary hearing. It should simply establish what the investigation has found.
Handing the Matter to a Disciplinary Hearing
Where the investigation finds that there is a case to answer, the matter should be referred to a formal disciplinary hearing. The hearing should be conducted by someone other than the investigator. The employee should be given reasonable advance notice of the hearing, provided with copies of the investigation report and supporting evidence, and informed of the potential outcomes.
Common Mistakes That Undermine Investigations
- Investigating officer is too close to the situation to be genuinely independent
- Witnesses are interviewed together or allowed to discuss the matter before their individual interview
- Leading questions used in witness interviews that steer towards a particular conclusion
- Investigation scope is too broad, too narrow, or changes partway through
- No written report produced — just a verbal summary passed to the decision-maker
- Decision on outcome made before the formal disciplinary hearing has taken place
When to Get External Support
Complex investigations — particularly those involving allegations of discrimination, harassment, or senior employees — carry significant legal risk. Bringing in an external HR consultant to conduct or oversee the investigation provides independence, expertise, and a much stronger position if the matter is later challenged.
Clear Path Solutions conducts independent workplace investigations for UK employers and provides HR support throughout disciplinary and grievance processes. Contact us: sales@clearpathuk.co.uk | 07544 732980
