It is becoming increasingly common for employees to raise grievances at work. Research published by Acas in November 2025 found that 44% of people in Great Britain experienced conflict at work between November 2024 and November 2025, with the most common topics of conflict being capability and performance, personal disagreements and relationship issues, and bullying, discrimination and harassment.
In most cases, grievances will be handled internally by the employer, usually with support from HR and in accordance with the employer’s grievance procedure. An impartial and independent person, with the requisite training, should be appointed as the investigator. Employers should ensure that grievances are addressed and investigated appropriately and proportionately, having regard to their internal policies and the Acas Code of Practice.
However, where matters are complex, sensitive, time-consuming or involve senior individuals, appointing an independent external investigator may be more effective and cost-efficient. This article explains what a “good” employer-led investigation looks like and considers when external support may be beneficial.
What does a good investigation look like?
A good investigation should be prompt, objective, proportionate and thorough. It should follow the employer’s own policies and procedures, as well as the Acas Code of Practice.
The investigation should aim to gather relevant evidence from those who have knowledge of the matters leading to the grievance, find out whether there is a case to answer, ensure everyone involved is treated fairly, and help the decision-makers reach an informed decision.
Preparation and planning – It will often be necessary to meet with the complainant at an early stage to understand the grievance, request supporting evidence, and invite them to suggest relevant witnesses. This will help the investigator to identify clearly the scope of what is to be investigated. The employer’s internal policy should be followed, including any right to be accompanied, and reasonable adjustments should be considered where the complainant has a disability.
Evidence gathering – Once the scope of the investigation has been determined, the investigator should start gathering evidence relevant to the grievance. Depending on the nature of the complaint, this may include documents, emails, Teams or other messages, HR or personnel records, policies, meeting notes, CCTV or other video footage, audio recordings, access logs, screenshots and other electronic material. The investigator should also interview the person or persons complained about and any other individuals who have knowledge of the matters under investigation. It may then be necessary, although not always, to re-interview the complainant to clarify particular points. It is important to maintain confidentiality throughout this process and to regularly remind interviewees of this.
Assessment and reporting – Once the investigator has collected all relevant information, they should assess what they have found objectively on the balance of probabilities, considering whether it is more likely than not that the events that were the subject of the grievance occurred. The investigator should compile their findings into a detailed investigation report. The report should summarise the complaint, set out relevant background information, identify who was interviewed, outline the main evidence considered, and then make findings or conclusions in respect of each allegation. The report should be handed to the employer’s HR manager or other person responsible for deciding the outcome of the investigation, so that the outcome can be communicated to the complainant. It is generally advisable for the complainant to be provided with a copy of the report.
What happens if you get it wrong?
An employer may face a number of consequences if it fails to conduct a good investigation into a grievance.
If the employee decides to take the employer to the Employment Tribunal and the Tribunal finds that the employer did not follow the Acas Code of Practice during the investigation, the Tribunal can increase the employee’s award by 25%. For example, in R March v Whipcoot Developments Ltd and Whipcott Getaways Ltd: 1401320/2022, the claimant was awarded an Acas uplift of 15%. The claimant had been unfairly dismissed after her employment was transferred to a new employer and she raised a grievance which the new employer failed to respond to.
If the grievance involves allegations of discrimination, employers should be particularly careful to ensure that the way in which the grievance is handled does not in itself give rise to another claim of discrimination.
When might an external investigator be appropriate?
Although most investigations are appropriately carried out internally, an employer may decide to appoint an independent external investigator where the matter is complex, sensitive, time-consuming, involves senior individuals, or where the employer does not have the time or expertise in-house to deal with it effectively. External support can also be useful where HR may be involved in the matters complained about or where internal views have become entrenched.
Appointing an external investigator may help guard against conflicts of interest or perceptions of bias, give all parties greater confidence in the process and outcome, and produce a well-structured report which is easier to explain and defend if later challenged. In appropriate cases, this may save time, costs and stress in the long run.
If you would like to discuss any of the issues raised in this article or you would like assistance with an investigation, please contact Ed Henderson or Reshma Derasari.