Corporate investigations: same facts, new law – would the 24 November 2025 Cassation ruling be the same under the Belgian Private Investigations Act?

Today marks the first anniversary of the entry into force of the new Belgian Private Investigations Act (the 2024 Act), which has been a turning point for how corporate investigations are conducted in Belgium.

The shift brought about by the 2024 Act becomes clear when contrasted with a recent ruling of the Belgian Court of Cassation of 24 November 2025. That decision, which still applied the former Act of 19 July 1991 on private detectives (the 1991 Act), offers an interesting test case: a scenario that previously required complex debate on whether a private investigation report was admissible can now be dealt with in a far more straightforward way under the 2024 Act.

The Court of Cassation ruling of 24 November 2025

In the contested judgment before the Court of Cassation, the Mons Labour Court ruled on a case where a victim of a workplace accident, suffering from long‑term incapacity, had been the subject of a private investigation carried out by two investigators engaged by an insurer. The investigators mainly observed the victim’s movements in public spaces and noted a discrepancy between those observations and the degree of incapacity officially recognised.

Before the Mons Labour Court, the admissibility of the investigation report was challenged on two main grounds: (i) it was disputed whether the investigators were duly authorised private detectives under the 1991 Act, and (ii) the insurer had unlawfully refused to disclose the investigation mandate. The court upheld both objections, found that the 1991 Act had been breached, and consequently decided to disregard the investigation report as unlawful.

The Court of Cassation quashed such judgment because the Mons Labour Court had failed to apply the (Antigone) test developed by the Court of Cassation for determining whether an illegally obtained piece of evidence may nonetheless be admitted in civil proceedings. Under that test, the Court must (i) first verify whether there is a specific statutory provision governing the use of the unlawfully obtained evidence; and (ii) in the absence of such legal provision, the Court must then examine (ii.a) whether the illegality affects the reliability of the evidence, or (ii.b) whether the use of that evidence is compatible with the right to a fair trial.

How would the case be assessed under the 2024 Act?

Issue 1: private investigation report prepared by unauthorised parties: the 2024 Act explicitly provides for the nullity of an investigation report drawn up by a private investigations company or in‑house investigations service that is not duly authorised by the Belgian authorities (Art. 101 of the 2024 Act in conjunction with Art. 7). The legislator’s intention is clear: by attaching nullity to such breach, the 2024 Act is designed to have a self‑regulatory effect, as any investigation report prepared in violation of this provision becomes unusable. If the Mons case were decided under the 2024 Act and the private investigators were not duly authorised, the court would now be obliged to disregard the investigation report.

In addition, the company which uses such unlicensed private investigations company or in house investigations service faces a possible administrative fine of up to EUR 15,000 (Art. 8 of the 2024 Act). This possible sanction is a deliberate policy choice by the legislator, based on the observation that “practice has shown that many illegal acts are committed with the knowledge and consent of the service user”, hence the necessity to sanction the party requesting the private investigation.

Issue 2: obligation to share the document describing the investigation mandate: Here too, the 2024 Act provides a clear answer: where the results of a private investigation are submitted to a Court, that Court may order that a full copy of the investigation file be produced (Art. 101 of the 2024 Act). Once again, if the Mons case were decided under the 2024 Act, the document describing the investigation mandate would have had to be produced upon the court’s express request. 

Conclusion

As illustrated by the above analysis, the 2024 Act is a game changer. One year after its entry into force, the time has come to be fully up to speed with this new regime. Your usual Freshfields contact will be pleased to guide you through this legal framework and help ensure that your private investigation reports are legally sound and can be reliably used before Belgian courts.