Employee Disciplinary Process: ACAS-Compliant UK Guide

Every employer will eventually face a situation where an employee's conduct or performance falls below acceptable standards. How you handle it determines whether the outcome is fair, defensible, and legally compliant — or whether it becomes an employment tribunal claim. The ACAS Code of Practice on Disciplinary and Grievance Procedures is the benchmark that tribunals use to judge whether your process was reasonable.

This guide walks you through each stage of the disciplinary process, from investigation through to appeal, with practical advice on avoiding the most common procedural failures.

Why the ACAS Code matters

The ACAS Code of Practice on Disciplinary and Grievance Procedures is not legally binding in itself, but tribunals are required to take it into account when deciding unfair dismissal and related claims. If you unreasonably fail to follow the Code, a tribunal can increase any compensation award by up to 25%.

Conversely, if you follow the Code and act reasonably at each stage, you have a strong defence even if the employee disagrees with the outcome.

The ACAS Code: key principles

The Code establishes several fundamental principles that must underpin your entire process:

1. Establish the facts through investigation before taking any action
2. Inform the employee in writing of the allegations against them
3. Hold a meeting to discuss the matter, giving the employee a chance to respond
4. Allow the employee to be accompanied at any formal meeting
5. Decide on the appropriate action based on the evidence
6. Provide the employee with a right of appeal against any formal sanction

Stage 1: Investigation

Before any disciplinary meeting, you must investigate the matter thoroughly. The purpose is to establish the facts, not to prove guilt.

Who should investigate

The investigator should ideally be someone different from the person who will chair the disciplinary hearing. In small businesses where this is not practical, the same person can do both, but take extra care to approach the hearing with an open mind.

What the investigation should cover

Gather all relevant evidence, including witness statements (taken in writing), documentary evidence such as emails, records, CCTV footage, the employee's personnel file and any previous warnings, and any relevant policies or procedures.

Interview the employee under investigation — this is an investigation meeting, not a disciplinary hearing. The employee does not have a statutory right to be accompanied at an investigation meeting (though allowing a companion is good practice).

Suspension

In serious cases, you may need to suspend the employee during the investigation. Suspension must be on full pay unless the contract expressly permits unpaid suspension (which is rare and generally inadvisable). Suspension should be a neutral act to facilitate the investigation, not a punishment. Review the suspension regularly and keep it as short as possible.

Stage 2: The disciplinary letter

If the investigation reveals a case to answer, write to the employee setting out the allegations. The letter must include a clear description of the alleged misconduct or performance issue (with sufficient detail for the employee to understand the case against them), the date, time, and location of the disciplinary hearing, the employee's right to be accompanied, copies of all evidence that will be relied upon at the hearing, and a statement that a possible outcome could include a formal warning or dismissal (depending on the seriousness).

Stage 3: The disciplinary hearing

Timing

Give the employee reasonable time to prepare — ACAS recommends at least 5 working days between receiving the letter and the hearing. Allow reasonable postponements if the employee or their companion cannot attend.

The right to be accompanied

Under Section 10 of the Employment Relations Act 1999, workers have a statutory right to be accompanied at any disciplinary hearing that could result in a formal warning or other disciplinary action. The companion can be a trade union representative or a fellow worker. The companion can address the hearing, sum up the employee's case, and confer with the employee, but cannot answer questions on their behalf.

Running the hearing

A fair hearing follows a structured format:

1. Introduce the purpose of the meeting and the people present
2. Set out the allegations and the evidence gathered during the investigation
3. Allow the employee to respond to each allegation — listen carefully and take notes
4. Ask questions to clarify any points
5. Allow the employee's companion to make representations
6. Adjourn to consider the evidence before making a decision

Stage 4: The decision

After adjourning and considering all the evidence, decide on the appropriate outcome. The decision must be communicated in writing and should set out the allegations, the evidence considered, the employee's response, your findings on each allegation, the sanction (if any), the reasons for the sanction, and the right of appeal.

Available sanctions

Gross misconduct

Summary dismissal — dismissal without notice — is only appropriate in cases of gross misconduct. Examples commonly recognised include theft or fraud, physical violence, serious breach of health and safety rules, serious insubordination, and bringing the organisation into serious disrepute.

Even in gross misconduct cases, you must still follow a fair process: investigate, hold a hearing, and allow an appeal. The seriousness of the allegation does not excuse a shortcut in the procedure.

Stage 5: The appeal

Every employee who receives a formal disciplinary sanction must be offered the right to appeal. The appeal is not optional — failing to offer it is a clear breach of the ACAS Code.

Who hears the appeal

Ideally, the appeal should be heard by a more senior manager who was not involved in the original decision. In very small businesses, this may not be possible — in that case, consider using an external HR consultant or a director who was not involved.

Scope of the appeal

The appeal can review the original decision on any grounds, including that the finding was wrong on the evidence, the sanction was disproportionate, the process was procedurally unfair, or new evidence has come to light. The appeal is a rehearing or review, not just a rubber-stamping of the original decision. The appeal manager must genuinely consider the grounds of appeal and can overturn, reduce, or uphold the original sanction.

Outcome

Communicate the appeal outcome in writing. The decision at appeal is final — there is no statutory right to a further appeal.

Special considerations

Disciplinary action during probation

Employees in their probation period have the same right to a fair process as any other employee. While employees with less than 2 years' service generally cannot bring an unfair dismissal claim, they can claim automatic unfair dismissal (for protected reasons such as whistleblowing or pregnancy), discrimination, and wrongful dismissal (failure to give notice). Always follow a fair process regardless of service length.

Overlap with grievance

If an employee raises a grievance during disciplinary proceedings, consider whether the grievance is related to the disciplinary matter. If it is, you may need to pause the disciplinary to deal with the grievance first. If the grievance is unrelated, both processes can run in parallel.

Sickness absence during disciplinary

If an employee goes off sick during disciplinary proceedings, you can continue the process. Obtain medical evidence about whether they are fit to attend a hearing, offer reasonable adjustments (such as a written submission or a companion attending on their behalf), and postpone once or twice, but do not allow indefinite delays. Ultimately, you can proceed in the employee's absence if they are unable or unwilling to attend after reasonable adjustments have been offered.

Record keeping

Maintain comprehensive records of every stage of the process. These records are essential evidence if the matter reaches a tribunal.

Keep investigation notes and evidence, the disciplinary letter, notes from the hearing, the decision letter, appeal correspondence and notes, and any related documents such as medical evidence or occupational health reports.

Retain these records for the duration of employment plus at least 6 years (the limitation period for most legal claims). Handle all records in accordance with UK GDPR requirements.

Frequently asked questions

Next steps

Key takeaways

A fair disciplinary process follows a clear sequence: investigate thoroughly, put the case to the employee in writing, hold a hearing where they can respond, make a reasoned decision, and offer an appeal. Follow the ACAS Code at every stage, document everything, and apply sanctions consistently. The process protects your business from tribunal claims — and it produces fairer outcomes for everyone involved.

If the disciplinary process leads to dismissal, make sure the final pay is handled correctly through your payroll. Use our Payroll Tax Calculator to calculate the final pay run including any outstanding annual leave payments.