How to Conduct a Disciplinary Investigation

A disciplinary investigation is the fact-finding stage that should take place before an employer decides whether formal disciplinary action is justified. Its purpose is not to build a case against the employee. It is to establish, as fairly and objectively as reasonably possible, what happened and whether there is a disciplinary case to answer.

The current Acas Code says employers should carry out any necessary investigation to establish the facts and should do so without unreasonable delay. In misconduct cases, different people should conduct the investigation and disciplinary hearing where practicable.

This guide concentrates on the investigation itself. Our wider disciplinary procedure for employers explains the stages that may follow if there is a case to answer.

What is a disciplinary investigation?

An investigation is the employer’s process of gathering and assessing relevant information about an allegation or workplace incident.

Depending on the circumstances, it may involve reviewing documents, emails, messages, CCTV or other records; speaking to witnesses; meeting the employee concerned; checking workplace policies; and producing an investigation report.

The amount of work required should reflect the issue being investigated. A straightforward allegation might need only a small amount of evidence. A serious, disputed or multi-witness allegation may require considerably more.

Acas describes an investigation as finding out all that can reasonably be established about the issue, gathering evidence from all sides and helping the employer decide what should happen next. The investigator should not start from an assumption of guilt.

Who should conduct the investigation?

Choose someone who can approach the matter impartially and has sufficient experience for the seriousness and complexity of the allegation.

That might be another manager, a member of HR or, in an appropriate case, an external HR professional.

Ideally, the investigator should not already be involved in the events being investigated. Acas also recommends using different people for the investigation, disciplinary hearing and appeal where possible. Smaller employers may not always have enough managers to achieve complete separation, in which case the priority is to make the process as impartial as reasonably possible.

An external investigator can be useful where there is a genuine conflict of interest, the allegations involve senior management, the facts are particularly sensitive or the organisation lacks suitable internal expertise. It is not necessary for every difficult case, and appointing an external consultant does not automatically make an investigation legally “independent”.

Where an employer wants experienced HR support to conduct or participate directly in workplace processes, Harrington Raine’s HR Consultancy & Meeting Support service can provide additional hands-on assistance.

Step 1 — Define the allegation and scope

Start by being clear about exactly what is being investigated.

An allegation such as “poor conduct” is usually too vague. Instead, identify the specific behaviour, approximate date or period, people involved and the rule, standard or expectation that may have been breached.

For example:

“On 4 September, it is alleged that [employee] used threatening language towards [colleague] during a meeting in the warehouse.”

A clear allegation helps the investigator determine which evidence is relevant and gives the employee a meaningful opportunity to respond.

It is also important not to decide the outcome when drafting the allegation. Even where the conduct could potentially amount to gross misconduct, that describes the possible seriousness of the allegation; it does not remove the need for an appropriate investigation and disciplinary process. The current Acas Code expressly states that a fair disciplinary process should still be followed before dismissal for gross misconduct.

If genuinely new allegations emerge during the investigation, consider whether the scope should be expanded or a separate allegation opened. The employee should normally be told what additional matter is being investigated and given a reasonable opportunity to respond to it.

Step 2 — Plan the investigation

For anything beyond the simplest matter, prepare a short investigation plan.

It should usually identify:

• the allegation and terms of reference;
• who is investigating;
• the relevant policies or standards;
• documents and records that may need to be obtained;
• potential witnesses;
• the employee or employees who need to be interviewed;
• evidence that could disappear or become unavailable;
• the likely sequence of interviews;
• any confidentiality considerations; and
• an indicative timetable.

Acas specifically recommends planning investigations and considering evidence such as work records, emails and CCTV, as well as practical deadlines such as CCTV deletion periods or witnesses going on leave.

The plan is a starting point rather than a script. Investigations frequently develop as new information becomes available.

Should the employee be suspended?

Suspension should not be automatic merely because an allegation is serious.

Where suspension is considered necessary, the current Acas Code says it should be as brief as possible, kept under review and made clear that suspension is not itself disciplinary action. Employers should also consider whether less disruptive alternatives could adequately manage the risk.

Step 3 — Gather relevant evidence

Collect the evidence reasonably necessary to understand what happened.

Depending on the allegation, this could include:

• emails and workplace messages;
• documents and records;
• rotas, access logs or timesheets;
• policies and procedures;
• CCTV;
• telephone or system records;
• photographs;
• previous correspondence relevant to the event; and
• information identified by witnesses or the employee.

Do not collect only material that supports the allegation. The investigator should follow evidence that may support or undermine it.

Equally, an investigation is not an unrestricted search through an employee’s working life. Evidence gathering should remain relevant and proportionate to the issue.

Emails, messages and CCTV

Workplace information is also personal data, so employers need to consider data protection requirements when obtaining or using it.

The ICO says monitoring must have a clear purpose and must be necessary and proportionate. Employers should not simply collect information “just in case”, and particular care is required when accessing emails, messages, CCTV or information that may contain private or special-category data.

Existing workplace monitoring policies, privacy information and the circumstances in which the evidence was obtained will therefore matter.

Step 4 — Interview witnesses

Speak to people who have information that is genuinely relevant to the allegation.

Use open and neutral questions initially:

• What happened?
• Where were you?
• Who else was present?
• What did you see or hear?
• What happened immediately before and afterwards?
• Is there anything that might help verify your account?
• Is there anyone else you think we should speak to?

Follow-up questions can then test unclear points or inconsistencies.

Notes should be sufficiently detailed to record the substance of the evidence. Acas recommends allowing witnesses to check their statement and normally sign it as confirmation of accuracy. A refusal to sign does not automatically mean the evidence must be disregarded; the investigator should record the refusal and, where possible, the reason.

If many people witnessed essentially the same incident, it is not automatically necessary to interview every person. Acas says a sample may be sufficient where accounts are broadly consistent, although further witnesses may be needed where information conflicts or important gaps remain.

What if a witness asks to remain anonymous?

Anonymous evidence should be approached cautiously.

Acas recommends avoiding anonymous witness statements where possible because the employee should ordinarily have a fair opportunity to understand and challenge evidence against them. Anonymity may sometimes be appropriate in exceptional circumstances, for example where there is a genuine fear of retaliation.

If anonymity is considered necessary, establish why, assess whether the concern is genuine, keep a full unredacted record internally and consider how much information can fairly be disclosed without identifying the witness.

The more important the anonymous evidence is to the eventual decision, the greater the need for care.

Step 5 — Hold an investigation meeting with the employee

The employee concerned should normally have an opportunity to give their account before the investigation is concluded.

This meeting is for fact-finding. It should not quietly turn into the disciplinary hearing.

Explain the purpose of the meeting, the investigator’s role, the allegation being investigated and the importance of confidentiality. Ask neutral questions and give the employee a proper opportunity to explain what happened, identify evidence and suggest relevant witnesses.

Acas recommends interviewing the employee at an early stage in potential disciplinary investigations because their account can identify which facts are genuinely disputed and help focus the remaining investigation.

Do not treat a refusal to answer a particular question as automatic evidence of misconduct. Record the refusal and continue to assess the evidence that is available.

Does the employee have a right to be accompanied?

There is currently no general statutory right to be accompanied at a disciplinary investigation meeting. The statutory right applies to qualifying disciplinary hearings where formal disciplinary action may result or be confirmed.

However, an employer’s own procedure may provide a right to accompaniment, and Acas considers allowing accompaniment at an investigation meeting to be good practice. Reasonable adjustments may also mean permitting additional support for a disabled employee in appropriate circumstances.

Check the employer’s own policy before sending the invitation.

How much investigation is enough?

There is no standard number of interviews, documents or investigation days that makes a process fair.

The appropriate question is whether the employer has taken reasonable steps to establish the important facts in the circumstances.

Consider:

• the seriousness of the allegation;
• how strongly the facts are disputed;
• the potential consequences for the employee;
• how many people were involved;
• whether important evidence conflicts;
• whether an obvious source of evidence remains unchecked; and
• whether further enquiries are likely to add anything meaningful.

A minor and largely admitted incident may require relatively little work. Alleged dishonesty involving disputed records and several witnesses may require considerably more.

The objective is a sufficiently reliable factual basis for the next decision — not a court-style exercise designed to investigate every theoretical possibility.

Complications during an investigation

The employee is off sick

Sickness does not automatically stop an investigation indefinitely.

First consider whether the meeting can reasonably be rearranged or adapted. Alternatives might include a remote meeting, a different location, additional breaks or written questions.

Where appropriate and with the employee’s permission, medical information may help establish whether they are fit to participate and whether adjustments would assist.

If the employee remains unable or unwilling to attend, Acas says the employer may ultimately need to proceed on the available evidence, provided the investigation is conducted as fairly as possible and the employee is told what is happening.

A witness refuses to cooperate

Explore why. The person may be concerned about confidentiality, retaliation or becoming involved in a dispute.

Explain the purpose of the investigation and how their evidence may be used. Do not promise confidentiality that cannot realistically be maintained.

If they still refuse, record the position and consider whether the facts can reasonably be established through other evidence.

The employee raises a grievance

Do not automatically abandon one process because another has started.

The current Acas Code says that a disciplinary process may be temporarily suspended to deal with a grievance, but where the issues are related it may be appropriate to deal with them concurrently.

The correct approach depends on what the grievance is about. A grievance alleging bias by the investigator may require a different response from an unrelated complaint about another workplace issue.

What should the investigation report contain?

Once the relevant enquiries are complete, record the investigation clearly.

A useful report will normally contain:

• the allegation and scope;
• who conducted the investigation;
• the steps taken;
• the people interviewed;
• the evidence considered;
• relevant facts that were established;
• important facts that could not be established;
• significant conflicting evidence;
• relevant mitigating or contextual circumstances;
• any limitations in the investigation; and
• the investigator’s conclusions and, where their remit allows it, recommendation for next steps.

Acas says the report should be objective, factual and concise, include the evidence gathered, and distinguish facts that were established from those that were not.

The investigator should not decide the disciplinary sanction. Their role is to establish the facts and, where required, indicate whether the evidence justifies further action.

That may mean recommending:

• no further action;
• additional investigation;
• informal action; or
• referral to a formal disciplinary hearing.

The eventual disciplinary decision belongs to the person authorised to conduct that stage.

What happens after the investigation?

If important information is still missing, carry out the necessary further enquiries.

If there is no disciplinary case to answer, the formal process should normally end and the employee should be told.

If there appears to be a case to answer, the matter can move to the disciplinary stage. The employee should then receive sufficient information about the allegation and relevant evidence to prepare their response before a disciplinary hearing.

Our disciplinary procedure for employers explains the wider process from investigation through hearing, outcome and appeal.

Employers dealing with a live or higher-risk matter can also obtain disciplinary support where advice, documentation or help managing the process is required.

Common disciplinary investigation mistakes

Deciding the outcome first

An investigation should test the allegation, not justify a conclusion already reached.

Using vague allegations

The investigator cannot sensibly establish facts if nobody can define what is alleged to have happened.

Looking only for incriminating evidence

Evidence that undermines the allegation can be just as important as evidence that supports it.

Ignoring an obvious witness or document

A gap involving potentially important evidence may call the reliability of the investigation into question.

Turning the investigation meeting into a disciplinary hearing

Keep fact-finding and decision-making separate.

Over-investigating

Do not interview ten people merely because ten people exist. Follow relevant lines of enquiry and stop when additional work is unlikely to improve the factual picture.

Keeping poor notes

Important conclusions should be traceable back to evidence.

Allowing unnecessary delay

Memories fade, people leave and electronic evidence can disappear. The Acas Code requires necessary investigations to be carried out without unreasonable delay.

Treating external involvement as automatically impartial

An external investigator still needs clear terms of reference, relevant competence and an objective approach.

Frequently asked questions

Should witness statements always be signed?

Usually, it is sensible to ask the witness to check and sign the notes or statement to confirm accuracy. Acas recommends this approach. But an unsigned statement does not automatically have to be excluded. If a witness refuses to sign, record that fact and the reason where known.

Can an investigation meeting be recorded?

It can be recorded where the employer’s policy allows it and the parties agree. Acas notes that recording can inhibit open discussion and says any recording should be agreed by everyone involved.

How long should a disciplinary investigation take?

There is no fixed statutory timeframe. It should proceed without unreasonable delay but remain sufficiently thorough and fair. Complexity, witness availability, sickness and the amount of evidence can all affect the timetable.

Should the investigator decide whether the employee is guilty?

The investigator should make factual findings and may, if their terms of reference permit, recommend whether further action is appropriate. They should not decide the disciplinary sanction or approach the investigation as an exercise in proving guilt.

Can we proceed if the employee refuses to attend?

Potentially. First make reasonable attempts to understand the reason, rearrange where appropriate and consider alternative arrangements. If the employee remains unable or unwilling to participate, the employer may have to make a reasonable decision using the evidence available.

How long should investigation records be kept?

There is no single UK GDPR retention period for disciplinary investigation records. Employers should have a defensible retention policy based on why the information is needed, applicable legal or regulatory requirements and the storage-limitation principle. Records should be kept securely and deleted or anonymised when they are no longer required.

Does an employee need two years’ service before we should investigate properly?

No.

As at 9 September 2026, the ordinary unfair-dismissal qualifying period in Great Britain is still generally two years. Under the Employment Rights Act 2025, that period is due to reduce to six months from 1 January 2027. Existing day-one protections, including discrimination and various automatically unfair dismissal protections, also remain important.

A reasonable investigation should therefore not be treated as something that matters only once an employee reaches a particular service threshold.

For further practical guidance across disciplinary, grievance, performance, absence and other workplace issues, see our HR & Employment Law resources.