The ACAS Code of Practice on Disciplinary and Grievance Procedures is the framework against which employment tribunals assess whether an employer has acted reasonably in conducting a workplace investigation and taking disciplinary or grievance action. It is not legally binding in a strict sense — employers are not required to follow it — but the practical consequences of unreasonable non-compliance are real and direct. A tribunal can uplift any compensatory award by up to 25% where an employer has unreasonably failed to follow the Code, and it can reduce an award by up to 25% where the employee has unreasonably failed to do so.
In practice, the Code sets the standard. Employers who follow it are in a defensible position. Employers who depart from it need to be able to explain why, and that explanation needs to hold up. In my experience, the investigations that produce the most costly tribunal outcomes are rarely those where the employer followed the Code but reached a wrong conclusion. They are those where the employer did not follow the Code, and where the procedural failures were then used to undermine findings that were otherwise correct.
This article sets out what the ACAS Code requires at each stage of a workplace investigation — what it recommends, what it expects of employers, and where the most significant compliance failures occur. It is a practical guide for HR directors, in-house legal teams, and managers responsible for conducting or overseeing workplace investigations.
What ACAS Recommends
The ACAS Code, supplemented by the more detailed ACAS Guide to Discipline and Grievances at Work, sets out a framework for managing workplace disciplinary and grievance matters that is built around three principles: prompt action, fair process, and proportionate outcome. These are not aspirational standards. They are the minimum that an employment tribunal will expect.
Prompt Action
The Code requires that employers act without unreasonable delay once a disciplinary or grievance concern has been identified. Delay between the discovery of a concern and the launch of an investigation, delay in completing an investigation once begun, and delay in communicating the outcome — all of these are assessed against the standard of what is reasonable in the circumstances. What is reasonable varies with the complexity of the matter, but the baseline expectation is that investigation and disciplinary processes should be completed within weeks rather than months, absent genuine operational reasons for longer timescales.
Delay has its own consequences beyond the tribunal risk. Witnesses’ memories deteriorate. Evidence becomes harder to obtain or reconstruct. The employment relationship — for both the complainant and the subject — is placed under a sustained uncertainty that itself creates legal risk. Acting promptly is not simply a compliance matter. It is the approach most likely to produce a reliable investigation and a defensible outcome.
Fair Process
The Code’s fairness requirements run through every stage of the investigation and disciplinary process. The employer must establish the facts before taking formal action. The subject must be informed of the concern against them and given the opportunity to state their case before any decision is made. The person conducting the investigation should, where possible, be different from the person making the disciplinary decision. The subject must be informed of the outcome, told of their right to appeal, and given the opportunity to be accompanied at formal hearings.
Each of these requirements is individually significant. In combination, they constitute a framework of procedural protection that reflects the principle that an employee should not be subjected to disciplinary action without a fair opportunity to understand what they are accused of and to respond to it. An investigation that satisfies all of the substantive requirements — a thorough evidence review, carefully conducted interviews, well-reasoned findings — but fails on one procedural element may still produce an unfair dismissal finding.
Proportionate Outcome
The Code requires that any disciplinary outcome be proportionate to the conduct found. This does not mean that gross misconduct must always result in dismissal — it means that the sanction must fall within the band of reasonable responses that a reasonable employer might apply in the circumstances. An employer who dismisses for a first instance of minor misconduct, or who imposes a final written warning for conduct that would ordinarily warrant only a first warning, has not acted proportionately, however thorough the investigation was.
Proportionality also requires consistency. Where similar conduct has been treated differently in the past — where colleagues have received lesser sanctions for comparable behaviour — the departure from that pattern needs to be explained and justified. An unexplained inconsistency is both unfair to the individual subject and indicative of a disciplinary process that is not being applied even-handedly.
Employer Obligations Under the ACAS Code
The Code translates into specific obligations at each stage of the investigation and disciplinary process. The following are the most significant from a practical compliance perspective.
Establish the facts before acting: the Code requires that employers carry out necessary investigations before taking disciplinary action. This means that a disciplinary decision must follow an investigation, not precede one. An employer who has decided on an outcome before conducting an investigation, and then treats the investigation as a formality to provide procedural cover, has not complied with the Code regardless of the quality of the investigation record.
Inform the employee of the allegation: the subject of an investigation must be told, in writing, what they are alleged to have done and what the potential consequences are if the allegation is substantiated. The notification must be sufficiently specific that the subject understands the case they are being asked to answer. Vague or general allegations — concerns about your conduct — do not satisfy this obligation.
Give the employee a genuine opportunity to respond: the opportunity to respond must be real, not procedural. It means giving the subject sufficient time and information to prepare their case, access to any evidence that will be relied upon, and a genuine hearing at which their account is considered before any decision is reached. A hearing at which the outcome has already been determined is not a genuine opportunity to respond.
Allow accompaniment at formal hearings: workers have a statutory right to be accompanied at any formal disciplinary or grievance hearing by a fellow worker or trade union representative. The right must be actively communicated to the employee — they cannot waive it by default through not being told it exists. Refusing a reasonable request for accompaniment at a formal hearing is a procedural failure.
Notify the employee of the outcome: the employer must inform the employee of the outcome in writing as soon as possible after the hearing. Where the outcome is dismissal, the written notification must include the effective date of termination, the basis for the decision, and the employee’s right of appeal.
Provide a right of appeal: every disciplinary outcome must include the right to appeal, communicated in writing at the time the outcome is notified. The appeal must be heard by a more senior manager than the person who made the original decision, or by someone who was not involved in the original process. The absence of an appeal right is an independent procedural failure regardless of the merits of the original decision.
Investigation Planning
The Code does not prescribe a specific planning methodology for workplace investigations. What it requires is that the investigation be reasonable — in scope, in the selection of the investigator, and in the steps taken to gather evidence. Planning is the mechanism by which that reasonableness is established before the investigation begins, rather than reconstructed after problems have emerged.
Appointing an Independent Investigator
The Code recommends that, where possible, a different person should conduct the investigation from the person who will hear the subsequent disciplinary case. It also requires that the investigator be someone who can approach the matter with genuine objectivity. In practice, those two requirements together mean that the investigator should have no prior involvement in the matter, no significant prior relationship with either party, and no stake in a particular outcome.
Where these conditions cannot be met internally — because the subject is too senior, because the organisation is too small, because the concern involves the HR function itself, or because a prior investigation has been challenged — external investigators provide the independence that the Code’s requirements make necessary. In serious misconduct cases, using an external investigator from the outset also insulates the investigation from the suggestion that it was shaped by internal dynamics, regardless of how carefully it was conducted.
[Internal link to: Workplace Investigations service page]
Terms of Reference
The Code does not specifically require terms of reference, but the discipline of producing them before the investigation begins is consistent with the Code’s overall requirements of clarity, fairness, and proportionality. Terms of reference that define the scope of the enquiry, identify the allegations under examination, and set out what the investigation is and is not asked to decide protect both parties by ensuring that the investigation has a clear and communicated remit.
Suspension
Where the employer considers that the subject’s continued presence at work during an investigation would be inappropriate — because of the risk to evidence, to other employees, or to the investigation’s integrity — suspension on full pay is available. The Code requires that suspension be as brief as possible, kept under review, and communicated to the employee in terms that make clear it is a precautionary measure rather than a disciplinary one. An extended suspension that is not kept under review, or that is communicated in a way that implies a predetermined outcome, does not comply with the Code.
Witness Management
The Code does not prescribe a specific approach to witness interviews, but its overall requirements — fairness, promptness, and a thorough evidence-gathering process — carry clear implications for how witnesses are managed. The most significant of these are sequencing, record-keeping, and confidentiality.
Sequencing: the order in which witnesses are interviewed is not addressed explicitly in the Code, but the principle of building the evidential picture progressively — interviewing those with peripheral knowledge first, the principal subject last — is consistent with the Code’s requirement for a reasonable and thorough investigation. An investigation that interviews the subject before the documentary evidence has been gathered, or before other witnesses have been heard, is unlikely to be regarded as having conducted a thorough investigation.
Record-keeping: the Code requires that a record be kept of the disciplinary or grievance process. For investigations, this means maintaining records of what evidence was gathered, what witnesses were interviewed, and what each interview produced. Interview records should be shared with the interviewee for review and, where they are willing to do so, confirmation. A contemporaneous record that has been reviewed and confirmed by the interviewee is significantly stronger evidence than one produced retrospectively or that the interviewee disputes.
Confidentiality: the Code does not address confidentiality in specific terms, but the principle of a fair investigation requires that the process be managed in a way that protects its integrity. Both parties should be instructed not to discuss the investigation with colleagues. Information about the investigation’s direction should not be shared informally. Where a breach of confidentiality occurs — because a party has spoken to colleagues, or because information has leaked through informal channels — that breach should be documented and its implications for the investigation’s integrity addressed.
Witness reluctance: the Code does not compel witnesses to participate in workplace investigations. Where a witness declines to be interviewed, that refusal should be recorded and the investigation should proceed on the basis of the evidence available. Where a key witness’s account is central to the investigation and they have declined to participate, that limitation should be acknowledged in the findings report, along with its implications for the investigation’s conclusions.
Reporting Requirements
The Code does not prescribe a specific format for investigation reports. What it requires is that the facts be established, that the subject be given the opportunity to respond to those facts, and that the outcome be communicated in writing. In practice, a written investigation report is the most reliable mechanism for satisfying all three requirements and for demonstrating compliance with the Code if the matter is subsequently challenged.
The report that the Code effectively requires — even if it does not use that language — is one that:
- Identifies the scope of the investigation and the allegations examined.
- Describes the evidence gathered and the methodology used to gather it.
- Sets out the findings in relation to each specific allegation, applying the balance of probabilities standard.
- Gives the reasoning behind each finding, including why conflicting accounts have been resolved in the way they have.
- Acknowledges limitations: evidence that was unavailable, witnesses who declined to participate, or matters that the investigation could not resolve.
- Does not make recommendations about sanction — the investigation’s role is to establish the facts; the disciplinary decision belongs to the employer.
The distinction between investigation findings and disciplinary recommendations is one of the most frequently misunderstood aspects of the Code’s requirements. An investigator who recommends dismissal in their report has assumed a function that belongs to the decision-maker, not the investigator. An investigation report that is used by the disciplinary manager as if it were the decision — rather than the evidentiary foundation for a decision — has conflated two separate stages of the process and exposed the outcome to challenge.
Common Mistakes in ACAS-Compliant Investigations
The following failures recur consistently across the tribunal decisions I have reviewed and the investigations I have been asked to review or remediate. Each is avoidable. Each is the kind of error that can turn a correct disciplinary outcome into an unfair dismissal finding.
Failing to inform the subject of the specific allegation before interviewing them: an investigative interview in which the subject does not know what they are alleged to have done before they are asked to respond is not a fair interview. It may produce an account that is incomplete or misleading, and it fails the Code’s requirement that the employee be given the opportunity to state their case in full.
Interviewing the subject before gathering documentary evidence: this is one of the most consistent investigative errors, and it produces a specific and avoidable problem: the investigator cannot test the subject’s account against the documentary record because they have not yet seen it. An interview conducted without knowledge of the documents is an interview in which the subject’s account cannot be properly scrutinised.
Using the same person to investigate and decide: the Code recommends separating these functions, and employment tribunals are alert to situations where the investigator and the decision-maker are the same person. Where it is genuinely impossible to separate these roles — in small organisations, or where the relevant individuals are unavailable — that limitation should be documented and the decision-maker should demonstrate that they have approached the decision independently of any prior conclusions.
Allowing the investigation to run without a defined scope: an investigation without terms of reference will expand to fill the available time, generate findings about matters the subject was not told were under examination, and produce a report that is difficult to use because it is not clear what questions it was asked to answer. Terms of reference are a basic planning tool that costs almost nothing to produce and prevents a significant class of avoidable problems.
Producing a report that recommends sanction: the investigation’s role is to establish facts. The decision about what to do with those facts belongs to the employer in the disciplinary hearing. A report that recommends dismissal, or that uses language implying a predetermined outcome, has overstepped its proper function and exposed the disciplinary decision to challenge.
Failing to notify the right of appeal: the right of appeal must be notified in writing at the time the outcome is communicated. It is not sufficient to allow the employee to request an appeal at a later stage. An appeal right that has not been formally notified does not comply with the Code, and its absence is an independent ground of procedural unfairness regardless of how well the rest of the process was conducted.
Treating the investigation as a formality once the decision has been made: the investigation must genuinely inform the disciplinary decision, not provide retrospective justification for a decision that was reached before it began. Employment tribunals are experienced at identifying the difference between an investigation that shaped the outcome and one that was designed to justify it, and they treat the latter as a failure of the Code’s fundamental requirements.
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