A workplace investigation is how an employer finds out the facts before deciding a disciplinary or grievance case. Acas says it should gather evidence from all sides, establish whether there's a case to answer, and be carried out by someone not involved in the issue. Skip it, or do it badly, and any decision that follows is likely to be unfair.
In the UK, the process is shaped by the Acas Code of Practice on disciplinary and grievance procedures, and tribunals look at whether an employer followed it fairly. The step-by-step guidance below comes from Acas's investigations guide, last updated 24 June 2026. The principles travel well to other countries too.
The six stages
| Stage | What happens | The detail people miss |
|---|---|---|
| 1. Decide to investigate | Confirm there's a possible disciplinary or grievance issue | You can still resolve it informally at any stage |
| 2. Prepare | Appoint an investigator and agree terms of reference and a plan | Start as soon as possible, while memories are fresh |
| 3. Gather evidence | Collect emails, records, CCTV and other physical evidence | Watch for time limits, such as records being deleted |
| 4. Hold investigation meetings | Speak to the worker and anyone involved | There's no legal right to a companion at a disciplinary investigation meeting, but allowing one is good practice |
| 5. Take witness statements | Notes reviewed and signed by each witness | You don't have to interview every witness to the same event |
| 6. Report | Facts established, facts not established, mitigation | The report should be shared with the worker |
Who should investigate
Acas says to choose someone who isn't involved in the case, such as another manager or someone from HR, to avoid a conflict of interest. For serious or complex cases, such as potential gross misconduct, discrimination or bullying, a more senior or experienced person may be better, and in exceptional circumstances an external consultant. In a disciplinary case, a different person should ideally handle the investigation, the hearing and any appeal. In a grievance, it's usually best for the person hearing the grievance to investigate.
Write terms of reference covering what's being investigated, whether recommendations are expected, how findings should be set out and who they go to. It keeps the investigation focused and quick.
Gathering evidence
The investigator's job, in Acas's words, is not to prove guilt but to get evidence from both sides, stay objective and keep the case confidential. Physical evidence might include:
- Emails and paperwork.
- Receipts and computer records.
- Phone records.
- CCTV recordings.
- Attendance records and vehicle trackers.
Any monitoring has to follow the law, including data protection and the employment contract, and respect the worker's privacy. Acas says employers should make it clear in advance if monitoring like this is in place and can be used in investigations.
How long it should take
As quickly as possible, but never at the expense of being thorough and fair. Acas's own range: a simple case might need only a day; a complicated one could take several weeks. Set a reasonable timescale, tell the worker, and if you need longer, explain the delay to everyone involved and record it in the report.
Running investigation meetings
- Invite the person in writing, with reasonable notice, the reason, and the date, time and place.
- Book a private room where you won't be interrupted.
- Tell them whether they can bring a companion and how to arrange it.
- At the start, explain who's present, the investigator's role, the purpose and the need for confidentiality.
- Take notes, and have the person review and sign them.
Here's the sourced insight that saves time: Acas suggests interviewing the worker under investigation early, because it shows which facts are really in dispute, and you can focus everything else on those. If the worker admits the allegations, you may not need to investigate as fully, though their explanation may still need checking.
Witness statements
A witness statement is usually the signed notes of an investigation meeting. Witnesses can amend their statements and should sign any changes. If someone refuses to sign, find out why; if it can't be resolved, include the statement anyway and note the refusal. Where many people saw the same incident, you can speak to some of them and check they're broadly saying the same thing, unless the accounts differ significantly.
The investigation report
The report should set out which facts were established, which weren't, and any mitigating circumstances. Acas warns that leaving information out could make the investigation unfair, and that the conclusions should be the investigator's own, even if HR advises. If recommendations were agreed in the plan, they should be one of formal action, informal action or no further action. Next steps usually follow your disciplinary procedure or grievance procedure.
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The verdict
A fair investigation is the cheapest insurance an employer can buy. Pick someone independent, write a short plan, collect evidence before it disappears, and report what you found and what you didn't. If the allegation could be gross misconduct, take extra care: that's exactly where a rushed investigation gets picked apart at a tribunal.
Frequently asked questions
What is a workplace investigation?
The process an employer uses to find out the facts of a disciplinary or grievance issue, by gathering evidence from all sides, before deciding what should happen next.
Who should carry out a workplace investigation?
Someone not involved in the case, such as another manager or someone from HR. For serious or complex cases, a more experienced person or, exceptionally, an external consultant.
Can I bring someone to an investigation meeting?
In a disciplinary investigation meeting there's no legal right to be accompanied, but Acas says it's good practice to allow it. In grievance meetings, workers have the right to a companion.
Does the employee get to see the investigation report?
Acas says the employer should share the report with the worker. Sensitive personal information about others can be removed or withheld where there's a good data protection reason, but leaving out relevant facts could make the investigation unfair.
Do I need to interview every witness?
Not always. Acas says that where many people saw the same incident, the investigator can talk to some of them and check they're broadly saying the same thing, unless there isn't enough information or the accounts differ significantly.
How long does a workplace investigation take?
It depends on the case. Acas says a simple case might take a day, while a complicated one could take several weeks.
