Employee Investigations – A Practical Guide for Handling Investigations in the Workplace

Would your last workplace investigation survive a tribunal asking these five questions?

1. Was the investigator genuinely independent from the decision-maker?
2. Was suspension necessary, or just the default reaction?
3. Did the employee know the specific allegation — not just “an issue”?
4. Was the standard of proof “balance of probabilities”, not “beyond doubt”?
5. Was the process reviewed and documented at every stage?

If you hesitated on any of those, it’s worth a closer look. From April 2026, employees have up to six months to bring an employment tribunal claim, longer exposure, more time for gaps to surface.

Getting it right

Few processes carry as much risk, for both employer and employee, as a workplace investigation. Get it wrong, and you risk an unfair dismissal finding, a tribunal compensation uplift of up to 25%, and lasting damage to reputation and trust across your team and beyond. Get it right, and you protect the organisation, treat people fairly, and build a decision that will stand up to scrutiny.

This guide sets out how to run a fair, thorough and legally defensible investigation under UK employment law, reflecting the ACAS Code of Practice on Disciplinary and Grievance Procedures and the wider legal landscape as it stands in 2026.

Why investigations matter legally

The ACAS Code is not itself legislation, but it carries real legal weight. Employment tribunals take it into account when deciding disciplinary and grievance claims, and where an employer has unreasonably failed to follow it, a tribunal can increase compensation by up to 25%. Conversely, an employee who unreasonably fails to follow the Code can see their award reduced.

Crucially, a flawed investigation can render an otherwise justified dismissal unfair. Tribunals don’t ask “did the employee actually do it?”  They ask whether the employer carried out as much investigation as was reasonable in the circumstances, reached a genuine and reasonable belief in the misconduct, and followed a fair process throughout. A weak investigation undermines all three.

What’s changing in 2026–2027

The Employment Rights Act 2025 is being implemented in phases. From April 2026, the standard employment tribunal time limit for most claims, including unfair dismissal and discrimination, extended from three to six months, giving employees longer to bring a claim and employers longer exposure to risk. A new Fair Work Agency has also been established with its own investigation and enforcement powers on matters like holiday pay and statutory sick pay. Day-one unfair dismissal rights (removing the two-year qualifying period) are expected from January 2027. The direction of travel is towards more scrutiny of process, not less, making a well-run investigation more important, not optional.

Our Recommended Process

At McLean HR we have extensive experience of conducting investigations in the workplace, below is our recommended step by step process:

Step 1: Decide whether an investigation is needed

Not every issue requires a formal investigation. Minor, straightforward matters can often be resolved informally, through a conversation, coaching, or mediation, which preserves working relationships and saves time. Reserve formal investigations for matters that could lead to disciplinary action, a grievance outcome, or where facts are genuinely in dispute.

Where you do proceed formally, act promptly. Delay damages the reliability of evidence and is itself something tribunals will criticise, but don’t let speed compromise fairness. The right pace is “without unreasonable delay”, not “as fast as possible.”

Step 2: Appoint the right investigator

The investigator should be impartial, sufficiently senior, and have had no prior involvement in the matter. In a small organisation this can be genuinely difficult, if no one internally is sufficiently distant from the situation, consider an external investigator (HR consultant or employment lawyer).

Whoever you appoint, be clear with them, and record in writing, that their job is to establish facts objectively, not to build a case, justify a predetermined outcome, or confirm a manager’s initial view. This distinction between fact-finding and fault-finding is the single most common area where investigations go wrong.

Separate the investigator from the eventual decision-maker wherever possible. The person who investigates should not usually be the person who chairs any subsequent disciplinary hearing.

Step 3: Consider suspension carefully

Suspension is sometimes necessary, for example, where there’s a risk to evidence, other staff, or the business, but it is a serious step, not a default. Best practice includes:

• Treating suspension as a neutral act, never a punishment or an assumption of guilt.
• Considering alternatives first: a temporary change of duties, location, or reporting line.
• Suspension normally being on full pay and contractual benefits, confirmed in writing with reasons given.
• Keeping it under active review and as short as possible.  Most investigations should conclude within two to four weeks; if it runs longer, tell the employee why.

Getting suspension wrong, using it reflexively, or letting it drag on unreviewed, is one of the most frequently criticised aspects of workplace investigations in tribunal decisions.

Step 4: Plan the scope before you start

Before any interviews take place, define:

• What exactly is being investigated, the specific allegation(s) or grievance, not a vague sense that “something’s wrong.”
• What evidence exists or needs to be gathered (documents, systems logs, CCTV, correspondence).
• Who needs to be interviewed, and in what order.
• A realistic timeframe, communicated to the employee at the outset.

A written investigation plan, even a short one, is one of the best protections you can build in as it shows a structured, proportionate approach if the process is later challenged.

Step 5: Gather evidence and interview witnesses

• Secure documentary evidence early, before it can be altered, deleted, or lost.
• Interview witnesses individually and take a written record of each interview, ideally agreed and checked back with the witness.
• Ask open, neutral questions. Avoid leading questions that suggest the answer you expect.
• Interview the subject of the investigation and give them a fair opportunity to respond to the specific allegations, not a vague accusation, but the detail of what is alleged, when, and on what basis.
• Remember there is no reliable concept of “off the record” in a formal investigation, anything said in an investigation meeting can feed into a later disciplinary hearing, and both parties should treat it that way.

Note that the statutory right to be accompanied applies to disciplinary and grievance hearings, not investigation meetings themselves, though many employers extend this as good practice, and it’s worth stating your position clearly in your policy.

Step 6: Apply the right standard of proof

In workplace investigations, the test is the balance of probabilities, is it more likely than not that the alleged conduct occurred, not the criminal standard of beyond reasonable doubt. The investigator’s job is to reach a reasonable, evidence-based view on this standard, and to present findings, not necessarily a final disciplinary decision.

Step 7: Write a clear, fact-based report

A good investigation report:

• Sets out the allegation(s), the process followed, and the evidence gathered.
• Distinguishes clearly between fact, evidence, and the investigator’s analysis.
• Reaches a reasoned conclusion on whether there’s a case to answer, without pre-judging any disciplinary outcome, which is a separate decision for a different person.
• Is proportionate: for a straightforward matter, a short report is entirely appropriate; over-engineering a report for a minor issue creates its own risks.

Step 8: Handle confidentiality and data protection properly

Investigations routinely involve personal and sometimes special category data. Keep information on a need-to-know basis, store it securely, and be mindful of UK GDPR obligations, particularly around retention periods and an individual’s right to access records via a subject access request. Be cautious about promising absolute confidentiality to witnesses; you can promise discretion but not guarantee that details will never need to be disclosed as part of a fair process.

Common pitfalls to avoid

• Combining investigator and decision-maker roles without good reason.
• Treating the investigation meeting as a disciplinary hearing — they serve different purposes and should be clearly distinguished in correspondence.
• Failing to put the specific allegations to the employee in enough detail for them to respond meaningfully.
• Letting suspension run on without review or explanation.
• Assuming smaller employers are exempt — the ACAS Code applies regardless of headcount, and proportionality relates to the complexity of the case, not the size of the business.
• Inconsistent treatment — handling similar allegations differently across employees without a justified reason is a significant discrimination and unfair dismissal risk.

A quick pre-investigation checklist:

• Is a formal investigation necessary, or can this be resolved informally?
• Has an impartial investigator with no prior involvement been appointed?
• Has suspension been properly considered against alternatives, and is it justified and time-limited?
• Is there a written investigation plan and realistic timeframe?
• Have the specific allegations been clearly identified and will they be put to the employee in full?
• Is there a plan for secure handling of evidence and personal data?
• Is the standard of proof (balance of probabilities) clearly understood by the investigator?

Final thought

A fair investigation isn’t a bureaucratic hurdle, it’s what allows an organisation to make decisions with confidence, protect employees from unfounded allegations, and withstand scrutiny if a decision is later challenged. With tribunal time limits extending and enforcement activity increasing under the Employment Rights Act 2025 reforms, the organisations that invest in getting this process right now will be the ones best placed to manage the risk ahead.

To find out how we can help your workplace, or for more information on our Dispute Resolution service, get in touch with us at info@mcleanhr.co.uk

Workplace Dispute Resolution, Conflict Mediation, Investigations | McLean HR