A workplace investigation establishes the facts of a complaint or allegation before anyone decides what to do about it. You run one in eight steps, from scoping the allegation and setting terms of reference to the report, the decision and the appeal. In Great Britain no statute fixes the timetable, but a tribunal will ask whether the investigation was reasonable.
The guidance here applies in England, Wales and Scotland. Northern Ireland has its own code and rules.
The steps here apply to disciplinary, grievance and conduct cases. Whistleblowing reports carry extra rules, covered in Confide's guide to conducting a whistleblowing investigation.
Imagine a manager who forwards a complaint to HR with a one-line note, "Can you deal with this?", at half past four on a Friday afternoon. It names a colleague, describes three incidents over two months, and asks what the company will do.
By Monday three mistakes have been made. The manager has already spoken to the person named, so their account has been rehearsed. The complaint has gone to four people who did not need to see it, and nobody has written back to the person who complained.
What a workplace investigation is and when one is required
The Acas Code of Practice on disciplinary and grievance procedures has been in force since 11 March 2015. It covers disciplinary situations, meaning misconduct and poor performance. It also covers grievances, the concerns, problems or complaints that employees raise with their employers.
Paragraph 5 of the Code says employers should carry out the necessary investigations without unreasonable delay to establish the facts. Paragraph 6 says that where practicable, different people should investigate and hear the case.
A tribunal must take the Code into account. Section 207A of the Trade Union and Labour Relations (Consolidation) Act 1992 lets it raise an award by up to 25 percent where an employer unreasonably failed to follow it. Acas updated its step-by-step guidance on investigations on 24 June 2026, and it puts the consequence plainly. Without a reasonable investigation, any decisions in the disciplinary or grievance case are likely to be unfair.
The standard is reasonable, not perfect. The Employment Appeal Tribunal held in Lamb v Teva in January 2026 that the tribunal was entitled to find that minor flaws did not make an even-handed investigation unfair overall. Leaving out the investigation altogether is a different matter. An employer that dismisses on a manager's say-so, without investigating, is likely to be found to have dismissed unfairly, although what the employee did can still reduce the compensation.
Who should investigate
Acas says the employer should get somebody not involved in the case to carry out the investigation. Where possible, a different person should handle each step: the investigation, the hearing and the appeal. That rules out both line managers and anyone who witnessed the events.
A useful test is whether the investigator could explain to a tribunal, under cross-examination, why they were the right person. The terms of reference should record that answer.
Bring in someone external when the allegation is against a senior person or the HR team itself, or when it may become a criminal matter. Do the same when the organization has nobody who is both competent and uninvolved. Confide's guide on structuring an investigations team covers building that bench.
Grievances are the exception. Acas says it is usually best for the person hearing the grievance to investigate it. The Code requires only that the grievance is raised in writing with a manager who is not its subject. Any appeal is heard, where possible, by a manager not previously involved.
How to run a workplace investigation in eight steps
Acas sets out six steps. The eight below follow the same order and give two decisions a step of their own: suspension and the report.
1. Decide and scope
Not every complaint needs a formal investigation. Record the decision with its date and reason, and write the allegation in neutral terms.
"It is alleged that the employee made comments a colleague found demeaning" is an allegation. "The employee bullied a colleague" is a finding, and nobody has made it yet.
Check whether the complaint is also a protected disclosure under section 43B of the Employment Rights Act 1996, which since 6 April 2026 includes sexual harassment. The Court of Appeal held in Chesterton Global v Nurmohamed in 2017 that a personal complaint can qualify if the public interest test is met. If it does, the whistleblowing rules apply as well.
2. Terms of reference
Acas says the terms of reference should explain the investigator's role and responsibilities. That means what needs to be investigated, the witnesses, the sources of evidence (such as work records, emails and CCTV) and the time limits.
One page is enough. Name the investigator, the person who commissioned the work, the allegations in neutral form, the timescale and the person the report goes to. Say what the investigator is not doing. They establish facts and recommend whether there is a case to answer, but they do not decide the sanction.
3. Plan the evidence
List what evidence exists and where it is held, such as emails, messages, access logs, rotas, CCTV, prior complaints and the personnel file. Secure first anything that is overwritten on a schedule, or that a subject who learns of the investigation could tidy up. Acas expects a written record of how and why each piece of evidence was obtained.
Interview the complainant first, then the witnesses, then the subject. That way the subject answers the full account rather than a partial one.
4. Suspension as the exception
The Code says suspension with pay should be as brief as possible and kept under review. Acas's suspension guidance, updated on 6 February 2025, is blunter. It says not to use suspension automatically, and to suspend only if there is no other option. Suspension does not mean an employee has done anything wrong.
Acas consulted on a draft revised Code from 30 July to 23 September 2026. The draft limits suspension to protecting the investigation, the organization, other staff or the worker, or meeting a legal requirement.
If suspension is merely convenient, move the subject, change the reporting line or restrict system access instead. If you do suspend, write down why and set a review date. Tell the employee in writing that it is not a sanction.
5. Interviews and the right to be accompanied
Section 10 of the Employment Relations Act 1999 gives a statutory right to be accompanied. It attaches to disciplinary and grievance hearings rather than investigatory meetings. Even so, allowing a companion at the investigation stage costs nothing and usually helps.
The companion is a trade union official or another of the employer's workers. If the companion cannot make the proposed time, the employer must postpone to a reasonable time the worker proposes within five working days.
In the interview itself, follow the Acas instruction to get evidence from both sides rather than try to prove guilt. Ask open questions, one topic at a time. Put the allegation to the subject in full and invite them to name their own witnesses and evidence. Take a contemporaneous note and ask the interviewee to confirm or correct it.
6. Evidence handling and confidentiality
Investigations are usually kept confidential, with one qualification from Acas: a worker may discuss the case with a trade union or workplace representative. Keep the file to the people who need it, with every document dated, sourced and in one place.
Confidentiality does not override data protection. A worker keeps the right of access to their personal data during a grievance, disciplinary or dismissal process. A subject access request made mid-investigation must be answered within one month, extendable for complex requests.
Exemptions for legal privilege and for other people's data, such as witness identities, can justify redacting or withholding specific material. Write every note as if the employee will read it.
Keep the file no longer than necessary, the principle in article 5(1)(e) of the UK GDPR. When you set the period, remember that a tribunal claim can follow three to six months after the act.
7. The report, what it should contain, and who sees it
The report is the document a tribunal reads first. Acas says it should contain the facts established, the facts not established, any mitigating circumstances, and all the evidence collected.
The report should reflect the investigator's own conclusions. Its recommendation is limited to formal action, informal action or no further action, and the investigator should not discuss sanctions.
A working investigation report template adds the following:
- the terms of reference
- the allegations in neutral form
- a chronology
- the evidence, with source and date
- a summary of each interview
- findings allegation by allegation, with the reasoning
- mitigating factors
- the recommendation
- the interview notes, as appendices
Acas says the employer should share the report with the worker. If a report would embarrass the organization when the subject read it, rewrite it rather than withhold it.
8. The decision and the appeal
The report goes to the person who hears the case. For a disciplinary, that is a hearing before a manager who was not the investigator. For a grievance, it is a meeting held without unreasonable delay under paragraph 33 of the Code, with the decision in writing and the right to appeal under paragraph 40.
The appeal is heard, where possible, by a manager not previously involved, with the outcome in writing.
Timing: what the law expects
No statute in Great Britain sets a number of days. The Code's phrase at every stage is "without unreasonable delay". Acas resolves the tension in a sentence: while an investigation should be completed as quickly as possible, it always needs to be thorough and fair.
The EU sets numbers, at least for whistleblowing reports. Article 9(1) of Directive 2019/1937 requires acknowledgment of receipt within seven days and diligent follow-up by an impartial person or department. Feedback must follow within a reasonable timeframe not exceeding three months from the acknowledgment.
Those limits apply only to reports within the Directive's scope. In our view they are a sensible benchmark for other investigations too.
The US sets no deadline, but its regulators have said what they expect. The Equal Employment Opportunity Commission's 2024 guidance on workplace harassment has since been rescinded. It said an investigation is prompt if conducted reasonably soon after the complaint. Starting the next day was prompt, and waiting two months without mitigating facts was not.
The same guidance said an investigation is adequate if it is sufficiently thorough to arrive at a reasonably fair estimate of truth, and run by an impartial party. Separately, the Society for Human Resource Management's 2017 benchmark is that resolving a grievance in 30 days is a good target.
The cost of getting it wrong
Acas published a study of the cost of workplace conflict, by Saundry and Urwin, on 11 May 2021. It put the cost at £28.5 billion a year for UK employers. That includes about 374,760 formal grievances a year at £951 each and about 1.7 million disciplinary cases at £1,141 each. It also includes about 32,700 tribunal claims, costing about £800 million in litigation.
Ignore the Code and the award can rise by up to 25 percent. Prejudge the case and the uplift is the least of the problem.
In Johal v Northern Lincolnshire and Goole NHS Foundation Trust, the tribunal decided liability on 16 July 2026 and remedy on 7 August 2026. It found that the investigation "was conducted in a manner to seek to validate the misconduct rather than to approach it in an even-handed manner". It found that the chief executive "had already determined that Mr Johal was surplus to requirements", and that the investigation "was deeply flawed". The award was £118,888.50, and every finding was about process.
The backlog is growing. Ministry of Justice statistics for April to June 2026, published on 20 October 2026, show 14,000 single claims received, up 28 percent on the year. In the same quarter 6,100 were disposed of, and 537,000 claims were open in total.
Investigation timeline: what Great Britain, the EU and the US expect
| Stage | Great Britain | European Union | United States |
|---|---|---|---|
| Acknowledge | No fixed period; the Acas Code says not to unreasonably delay meetings, decisions or confirmation | Seven days from receipt of a whistleblowing report, under Directive 2019/1937 | No fixed period; the EEOC's 2024 guidance, since rescinded, treated the next day as prompt |
| Start | As soon as possible, without unreasonable delay | Diligent follow-up by an impartial person or department | Reasonably soon after the complaint; two months without mitigating facts was not prompt |
| Feedback or outcome | Decision in writing without unreasonable delay, with the right to appeal | Within a reasonable timeframe not exceeding three months from the acknowledgment | No statutory limit; the SHRM benchmark is 30 days to resolve a grievance |
| Appeal | Without unreasonable delay, where possible by a manager not previously involved, outcome in writing | Not fixed by the Directive | No federal requirement; the employer's own procedure applies |
| Record keeping | No longer than necessary under the UK GDPR; a tribunal claim can follow three to six months after the act | No period in the Directive's reporting provisions; data protection law applies | Depends on the statute a claim would be brought under |
What changes in 2027
The Employment Rights Act 2025 received Royal Assent on 18 December 2025. For dismissals with an effective date of termination on or after 1 January 2027, the qualifying period for unfair dismissal falls from two years to six months. The cap on the compensatory award is removed from the same date.
A far larger share of the workforce will be able to claim, and the ceiling on what a badly run disciplinary can cost disappears.
The Code is changing with it. Acas's draft revised Code grows from 47 paragraphs to 95 and extends to workers. It adds informal resolution, restricts suspension to the protective grounds above, and allows a pause for mediation. Acas expects it in 2027, and until then the 2015 Code applies.
How Confide runs an investigation
Most of the mistakes in the Friday-afternoon example come from a complaint living in email. Confide's Incident Response module gives each matter one case record, holding the tasks, files, internal notes and follow-up. Every task has an owner and a deadline, and the case stays open until the work is done. If a user is named in a report, Confide automatically revokes their access to that case, and each access and action is logged.
Two AI agents can work from the case record if you turn them on. Sentinel answers questions across cases and cites the records it used. An investigator might ask whether the subject has been named before, then read the cited records before relying on the answer.
Compose drafts the investigation plan, the investigation summary and formal letters from the case, using your own templates. Your team reviews, edits and approves each draft. The investigator and the hearing manager still own the findings, the recommendation and the decision. Case records and investigation data are never used to train AI models.
Workplace investigation FAQ
How long should a workplace investigation take?
The law in Great Britain sets no number of days. The Acas Code requires the investigation, the meeting, the decision and the appeal to happen without unreasonable delay. Acas says an investigation should be as quick as possible while remaining thorough and fair.
The EU Whistleblowing Directive requires acknowledgment within seven days and feedback within three months. In the US, the Society for Human Resource Management (SHRM) suggests 30 days.
Who should carry out a workplace investigation?
Someone not involved in the case. Acas says that where possible different people should handle the investigation, the hearing and the appeal, although for a grievance it is usually best for the person hearing it to investigate. Bring in an external investigator when the allegation concerns a senior person or the HR team, or when nobody inside is both competent and uninvolved.
Can an employee be suspended during an investigation?
Yes, but only as the exception. The Acas Code says suspension with pay should be as brief as possible and kept under review. Acas guidance says it should not be used automatically, should only be used when there is no other option, and is not a disciplinary sanction. Suspend when the employee's presence would put evidence, witnesses or other people at risk, and record the reason and set a review date.
What should an investigation report contain?
Acas says it should contain four parts: the facts established, the facts not established, any mitigating circumstances, and all the evidence collected. The report should reflect the investigator's own conclusions. It should recommend formal action, informal action or no further action, without discussing sanctions. The employer should share it with the worker.
Does the employee have a right to see the evidence?
Largely, yes. Acas says the employer should share the investigation report with the worker, and the worker keeps the right of access to their personal data throughout a grievance, disciplinary or dismissal process. A subject access request must be answered within one month, extendable for complex requests. Exemptions for legal privilege or other people's data, such as witness identities, can justify redacting or withholding specific material, but not ignoring the request.
What to do with the complaint on your desk
Acknowledge it in writing today. Decide who will investigate and write their terms of reference. Secure the evidence that will not wait, and only then speak to the person named.
A tribunal will look at how the investigation searched for the answer, so keep a record of each step as you take it. Confide's Incident Response module can hold the next one in a single case, from the first email to the appeal.
