Practical tips for conducting a disciplinary investigation

Updated: 16 April 2026

Many managers will have to deal with misconduct by an employee. When doing so, a fair procedure should be followed, or any resulting dismissal could be deemed unfair by an employment tribunal, if the employee has more than 2 years’ service, or 6 months service from Christmas Day 2026.

This article explains how to carry out a fair investigation, with regard to the ACAS Code of Practice on Disciplinary and Grievance Procedures (the ACAS Code) and established by case law.

Carrying out a disciplinary investigation

The ACAS Code provides practical guidance on the fair conduct of investigations. Failure to follow any part of the ACAS Code does not make an employer liable to a claim. However, if an employee wins an unfair dismissal, discrimination or wrongful dismissal (notice pay) case, the tribunal can increase the amount of compensation awarded by up to 25%, if the employer has unreasonably failed to follow the ACAS Code. Employees who also unreasonably fail to follow the ACAS Code can have their compensation reduced, but this is far less common. The term 'reasonable' crops up a lot in this context, and the guiding star for an employer should always be to be seen to be acting 'reasonably'.

One of the key principles set out in the ACAS Code is that employers should carry out investigations promptly to establish the facts of a case. Although nearly every case will require an investigation, the amount of investigation required varies with each case, based on a number of factors, including the nature and gravity of the case, the size and resources of the employer, the state of the evidence and the potential consequences of an adverse finding to the employee.

Planning an investigation

If informal action has not resolved an issue, or if the issue is more serious, the employer will need to start a formal process. In relation to the investigation stage this will involve, among other things:

• Checking the requirements of the employer's disciplinary procedure regarding the conduct of investigations.
• Determining the scope of the investigation.
• Choosing an appropriate investigator.
• Keeping in mind the general requirement to have different individuals at each stage (that is, the investigation, disciplinary hearing and appeal hearing) in ascending seniority. Small, family-run companies may instruct external personnel but retain overall responsibility for the process.
• As far as possible, attempting to complete the investigation within any timescales set out in the applicable disciplinary procedure. Consequently, managers with significant planned absences should be avoided.

The allegations against the employee should be set out at the start of the process. Firstly, the content of the allegations will frame the investigation and its scope. Secondly, the employee should know the case against them. This principle applies at the outset of the investigation and any subsequent disciplinary hearing. It is also vital that any allegations are set out precisely, and that the evidence considered is only about that matter, for example, an allegation that '1. You shouted at the Production Manager in the canteen at around 3pm on Thursday 28^th February, and called her 'a bully' and 'an idiot', 2. On the same date, at around 3.10 pm you left work without permission before the end of your shift.' is very specific, whereas alleging 'Aggressive behaviour towards the Production Manager and leaving work without permission last week' would be unsatisfactory and unhelpful to the employer's prospects if it came to a Tribunal hearing.

However, an investigation may help an employer to frame the final allegations for a disciplinary hearing more precisely. As such any initial letter inviting the employee to an investigation meeting may frame the allegations in a slightly broader way than any subsequent letter inviting the employee to a disciplinary hearing.

If an investigation is needed, the employer must consider who should conduct the investigation. As a general rule, where practicable, there are three functions in a disciplinary: The investigating manager, the disciplinary manager and the appeal manager. Generally the investigating manager should not be senior to the disciplinary manager, and the appeal manager should be senior to both the investigation and disciplinary managers, so that there is no basis for considering that the decision-makers might be reluctant to go against a more senior manager. In many cases, the employee's immediate line manager may be the appropriate person to investigate. An alternative is to appoint a member of the human resources (HR) department to conduct the investigation, since they may have had training on the best way to conduct investigations (although this may make it more difficult for HR to advise on the process). In other cases, someone with specialist knowledge may be needed (for example, a finance manager if the allegations concern financial mismanagement). The investigator should ideally not be a key witness (unless this is completely unavoidable, for example in the case of a small employer).

When selecting the investigator, the employer should also consider who will conduct the disciplinary hearing, if one becomes necessary, and any potential appeal hearing, with the levels of relative seniority in mind.

Employers should keep an open mind when carrying out an investigation, looking for evidence that supports as well as weakens the employer's case. It will be very important to the fairness of any subsequent dismissal that an employer is not seen to have pre-judged the outcome. For example, where simmering tensions between two employees have broken out into 'hostilities' between them and the employer is investigating, look back to see the root of the problem and if the apparent victim has provoked the incident and to see if there is a long-standing unresolved incident that might have provoked the employee under investigation.

It is not always necessary for an employer to extensively investigate each line of defence advanced by an employee. However, where the allegations against the employee amount to criminal behaviour, they must always be the subject of the most careful investigation, because of the serious effect on the employee's reputation, and the potential damage to their ability to continue working in their chosen field.

Role of the investigator and HR

The role of the investigator is to establish the facts by reference to the available evidence. The investigator should gather and consider evidence about what did or did not happen, so the employer can understand if there is a case to answer. This is distinct from determining culpability or "guilt", which is something for the manager conducting the disciplinary hearing (not the investigator) to determine. For example, an investigator could establish that emails were sent between certain employees on certain dates, and potentially comment on the content of these emails, without going so far as commenting on who was to blame for what.

Where a disciplinary investigation has been unduly influenced by a third party, such as an HR department, this could compromise the fairness of the process and make any subsequent dismissal unfair. Consequently, HR advisers should ensure that any advice they give to the investigator is limited to questions of law, procedure and process, and does not stray into areas of culpability. A designated HR officer can act as the investigator. However, the wider HR team would need to refrain from interfering with their colleague's investigation.

Obtaining the evidence

Although some investigations will take more time than others, an investigator should conclude an investigation as soon as possible.

Usually an investigation will involve meeting with the person accused of misconduct. An investigation meeting is not a disciplinary hearing, and the role of the investigator is distinct from that of the disciplinary hearing chairperson.

Employees have no statutory right to be accompanied at an investigatory meeting, although a contractual disciplinary procedure may give them such a right.

Whether interviewing the employee accused of misconduct or a witness, accurate notes of the meeting should be made reporting as accurately as possible the questions asked and the responses.

Investigators should ask probing questions to elicit information but should not ask leading or closed questions, particularly if they appear to seek a response that would only support the employer's case. The investigator should approach such meetings with an open mind and avoid being led by any theories about the case.

Both the employee facing the investigation and witnesses should be reminded of the need to keep any information discussed confidential. However, bear in mind that an employee may have a companion at a disciplinary and would have to explain the situation to the companion in order for the companion to play as full a part as possible.

Consider whether any physical evidence is likely to exist. The type of physical evidence will depend on the issue. For example, any suspicion that the employee has disclosed confidential information to competitors may require a search of the employee's correspondence, files and emails. If the employee has a company mobile phone, checks may need to be undertaken regarding what numbers were dialled. It may be appropriate for the employer to review CCTV recordings, particularly when requested by the employee. Issues arising from the employee's right to privacy may need to be considered in this scenario. In particular, employers should avoid gathering material that is obviously personal, such as private emails and diary entries. Social media posts can often be a source of information, and are often 'public', but beware of relying too heavily on something posted in a private setting or group which has been revealed to an employer, sometimes by another colleague.

The use of private messaging services, such as WhatsApp, brings its own set of challenges. Emerging case law suggests that individuals using private messaging have a reasonable expectation of privacy. However, privacy depends on the type of worker sending the messages and whether they are subject to professional standards, codes of conduct, or work in a regulated work environment. For example, if an employee is a member of a WhatsApp group exclusive to colleagues the employer would usually be able to use such messages as evidence of any harassment.

The right to privacy may also be engaged where an employer relies on email correspondence as evidence, unless the employee lacked a reasonable expectation of privacy, e.g. in an email purely related to work on a work account, which is likely not to give any reasonable expectation of privacy.

It may be acceptable for the employer to rely on witness statements and related information provided to it from other sources, notably the police in more serious cases. However, employers should always ensure that they evaluate the information received from the police carefully and consider whether any parts of that information need to be revisited or require additional investigation.

What happens when an individual refuses to co-operate with an investigation?

As a starting point, an investigator should consider if there is a good reason for an employee refusing to co-operate. If it's an illness an investigator could rearrange the meeting or ask the employee to produce a witness statement instead.

However, some employees will simply be uncooperative. An employee has a duty to obey reasonable orders from their employer, and a general duty to co-operate with a disciplinary investigation. As such, if an employee refuses to attend investigation meetings, an employer may deal with the situation through its disciplinary procedure, and might well be entitled to both advise the employee that a lack of co-operation might lead to decisions being made on the available evidence and conclusions drawn about the lack of co-operation.

Ultimately, in such cases, the employer will need to consider whether it can continue with the disciplinary investigation without the employee's co-operation. The employer should be satisfied that the investigation is sufficiently thorough before taking disciplinary action, particularly if a likely outcome is dismissing the employee. The employer should also invite the employee to submit written evidence, such as a witness statement, as an alternative to a meeting if the employee refuses to attend a meeting. Occasionally an employer has no choice but to conduct a disciplinary investigation without the input or co-operation of the employee.

ANONYMITY FOR WITNESSES

Employees may be reluctant to provide witness statements for disciplinary cases for many reasons, from wanting a quiet life, not wanting to be seen as a 'snitch' or fear (well-founded or not) of reprisals. Generally, Tribunals do not approve of anonymous statements being used except in exceptional circumstances, for example when a group of employees in a warehouse were suspected of drug dealing at work, where there was an obvious basis for employees to fear reprisals from their colleagues. However, in cases where there are allegations of serious harassment, employers might have good grounds for anonymising statements.

Investigation report

It is often helpful for the investigating officer to prepare a report summarising the investigation, the allegations and the evidence available. Our employment law team can provide you with a template report should you require this.

Content of report

The ACAS investigations guide (non-mandatory) advises that an investigation report should include:

An introduction, setting out:

1. the name and job title of the person who authorised the investigation;
2. the name and job title of the person who conducted the investigation;
3. a brief overview of the circumstances that led to the investigation; and
4. the terms of reference of the investigation and if they were amended.

The investigation process followed, including:

1. how the investigation was conducted;
2. what evidence was collected;
3. whether any pieces of evidence could not be collected and why;
4. the names and job titles of all witnesses and why each witness was relevant to the matter;
5. whether any witnesses could not be interviewed and why; and
6. an explanation of why any witness's statement has been anonymised and providing any details of enquiry into their character and background.

The investigation findings, including a summary of the:

1. findings from all relevant documents;
2. key evidence from each witness statement;
3. facts that have been established and what facts have not been established; and
4. mitigating factors to consider, if any.
5. The report's conclusions, including the investigator's recommendations based on all evidence collected.
6. Copies of all documents and witness statements collected and referred to in the report.

Drawing conclusions and making recommendations

The investigator should restrict their conclusions to recommendations on whether the employer should take formal action, such as holding a disciplinary hearing. The investigator should not suggest a possible sanction or prejudge the outcome of the disciplinary hearing. With this in mind, the ACAS investigations guide suggests that an investigator should restrict recommendations to:

• Formal action (for example, a disciplinary hearing);
• Informal action (for example, training or coaching); or
• No further action.

A poorly drafted investigation report, where an investigator oversteps their duties and suggests possible sanctions, could be very problematic for an employer.

Is further action required?

Not every investigation will result in a disciplinary hearing. However, in accordance with the overarching principle of avoiding unreasonable delay, employers should act promptly in deciding whether a disciplinary hearing is warranted and, subsequently, inviting the employee to a disciplinary hearing.

The investigator's role does not always finish when any investigation report has been submitted. If new information comes to light following the completion of the investigation, this information should be shared with the manager conducting the disciplinary hearing. Failure to do so could result in any subsequent dismissal being unfair.

Once an investigator completes their investigation and submits any report, and in order to avoid perceptions of bias, their further involvement should generally be limited to the following:

• If appropriate, discussing the report in person with those they report to, with the focus being on whether any further steps are necessary.
• Attending a disciplinary hearing in a fact-giving capacity only.
• Contributing to any policy or procedure review resulting from the investigation findings.

SUSPENSION

Suspending an employee from work during an investigation is generally regarded as a very serious step and should not be taken lightly. The ACAS code recommends that suspension with pay should be kept under review and the employer should make clear that it is not itself a form of disciplinary action. An unjustified suspension could be grounds for a claim for constructive unfair dismissal if it is done without proper cause as a breach of trust and confidence, and can in exceptional cases lead to a claim for damages if psychiatric injury follows.

OVERLAPPING DISCIPLINARY AND GRIEVANCE PROCEDURES

It is by no means rare for an employee facing a disciplinary to raise a counter-allegation by way of a grievance, e.g. about the person complaining about them, or a manager during the process. The ACAS code indicates that if this occurs, the disciplinary process may be suspended to allow the grievance to be considered, and if the disciplinary and grievance are related, they might be considered together as part of a disciplinary hearing (if matters go that far). This may result in delay to the disciplinary investigation, but it helps the employer consider the whole picture and would be likely to be regarded as 'reasonable'. Disregarding a grievance is unlikely to help an employer in the long run.

PARTICULAR PROBLEM AREAS

Recordings – where investigation meetings are conducted with an employee or a witness, an employer may wish to record them. If this is done, it should be clear on what basis the recordings will be used, e.g. will the recording be transcribed and the written account be used the disciplinary, and will the original recording be provided to the employee? There may well be concerns that recordings could end up on social media and be effectively impossible to control from there.

Covert recordings – an employee might have made a covert recording which is relevant to a disciplinary matter, e.g. recording what an alleged harasser said, or showing an apparently amicable interaction between alleged harasser and victim after the incident. Generally in Employment Tribunals, which have deliberately lax rules of evidence, covert recordings can be used in evidence if they tend to prove something relevant to the case, e.g. what was said, or the tone of an interaction. If there are covert recordings, careful thought should be given to allowing an employee (or a complainant) to put them forward, so that the whole picture is given.

Improper motives for complaints – discrimination and getting at whistle-blowers - It is an unfortunate fact of life that sometimes, complaints are made about employees for improper reasons, not just personal hostility (which is bad enough) but also because of a discriminatory motive, or to try to engineer the dismissal of whistleblower. A well-known case against the Royal Mail involved a manager who was found to have contrived a case against a whistleblower to dismiss her in her probationary period, with the managers involved in the disciplinary being unaware of that manager's motive, but the employer was still liable for a whistleblowing dismissal. The best protection against such situations is a thorough investigation, a fair procedure and an open mind.

THE FUNDAMENTAL QUESTION

If a disciplinary process gets to be looked at in an unfair dismissal case, the fundamental issue for the Tribunal is whether the employer's conduct of the investigation fell within 'the range of reasonable responses' that the employer could have adopted in those particular circumstances. That means that there are not so much 'right or wrong' answers looking at the process overall, (but there may be with particular steps), rather the question is was this a reasonable investigation that an employer might have conducted in those circumstances, and if so, then for unfair dismissal, it will pass the test, provided the other steps are similarly reasonable.

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