Step by Step guide to Internal Investigations

Published on: 24/10/2023

#Discipline & Grievance

Conducting an internal investigation is a necessary and often daunting part of both grievance and disciplinary investigations. For employers faced with this hurdle, it can sometimes be difficult to know where to start, and to be sure that you are doing the right thing.

The below step by step guide is intended for employers, to help them know the right actions to take and when to take them.

Consider if a formal investigation is necessary

It might be that the situation, be it grievance or disciplinary, can be dealt with in an informal manner, through a conversation with the person or persons involved. It is important to check this point carefully though, as you do not want to fail to investigate a claim that ought to have been properly investigated.

Seek Legal Advice

This is something that all employers should consider when facing an investigation. They can be time-consuming and complicated, not to mention requiring that the investigating team remain independent. It is useful to get advice early, before any mistakes are made, so that you can be assured that you are doing the right thing.

Chose the investigator or investigating team

The investigator should be independent of the issues, and must have the relevant training to be able to investigate properly and make findings. If there is any potential for bias, this should be considered and a suitable alternative found. For example, if an employee’s manager is referenced in a grievance, then it would be appropriate for that manager’s manager or another independent manager to investigate a grievance to avoid bias.

It is a good idea for employers to ensure that they have a few members of management team who are properly trained in investigations from their legal advisers, so that they have the ability to step up if required.

Preparing a plan for the investigation

An investigator and their team should stop to think about what information they need to find out to be able to investigate the issue at hand. This may involve considering what evidence they need to see and who they should interview.

The investigator should also bear in mind that this plan may need to adapt as the investigation commences. It may be that more facts come to light that require a new witness to be interviewed or new evidence to be considered.

The investigation should be a fact-finding exercise. Part of the investigator’s job is to set out what facts cannot be confirmed as well as what can be confirmed.

Collect and review relevant documentary evidence

The investigator should seek evidence from a variety of sources, including the subject of the grievance or disciplinary. They should consider all forms of evidence, including emails, documents, messages and CCTV. All evidence should be looked at with an independent eye, and the investigator should consider evidence even if it goes against the conclusion they think they will draw. Investigators should also approach evidence with an open mind to avoid reaching pre-determined conclusions.

Plan and conduct witness interviews

The investigator should consider who needs to be interviewed. It is easy to make this list too long, and the investigator should try to ensure that they only interview people relevant to the issue.

The investigator also needs to ensure that they fact check assertions said to them as far as possible, and try to consider the credibility of the statements given to them.

In the interviews, the investigator should ensure that they take full notes of the interview, and that these notes are approved by the witness after the interview.

Investigators should remember that it is important that this process is confidential, and that they state this clearly to all people that they interview. In an internal investigation it is easy for rumours to spread in an office which can quickly lead to disruption and even to claims of victimisation if not handled properly.

Prepare a findings report

Once the investigator has seen all the relevant evidence, they should consider this and draw conclusions. They should draw separate conclusions for each of the issues at hand, and consider what further steps should be taken in light of these conclusions. The investigator may also decide to make recommendations to the organisation in respect of process issues as part of the outcome.


If these steps are followed the investigation should produce a thorough and fair result. However, all cases have their differences, so if you are concerned about an internal investigation please do get in touch with a member of the employment team and we would be happy to help.


This information is for guidance purposes only and should not be regarded as a substitute for taking professional and legal advice. Please refer to the full General Notices on our website.