In a judgment handed down on 21 April 2026, the Competition Appeal Tribunal granted Dr Maria Luisa Stasi’s application for a Collective Proceedings Order against Microsoft Corporation, Microsoft Limited and Microsoft Ireland Operations Limited. The claim is brought on behalf of UK businesses and organisations alleged to have been overcharged for licensing Microsoft’s Windows Server operating system on rival cloud computing platforms. Aggregate damages are estimated to exceed £1.7 billion.
Dr Stasi alleges that Microsoft abused its dominant position, contrary to section 18 of the Competition Act 1998 and/or Article 102 TFEU, through licensing practices relating to Windows Server and Microsoft’s Azure cloud platform. The claim concerns Microsoft’s alleged treatment of customers using Windows Server on rival cloud providers, including Amazon Web Services, Google Cloud Platform and Alibaba Cloud, and alleges class-wide loss by way of overcharge.
The judgment is of wider significance for collective proceedings practice following the Supreme Court’s decision in Evans v Barclays Bank plc [2025] UKSC 48. Applying the Supreme Court’s recent guidance on the choice between opt-in and opt-out proceedings, the Tribunal rejected Microsoft’s submission that the proceedings should be bifurcated into separate opt-in and opt-out classes. The Tribunal held that there was no clear parallel between the practicability assessment in Evans and the position of the proposed class members in this case, and certified the claim on an opt-out basis.
Microsoft also resisted certification on the grounds that the claim lacked an adequate blueprint to trial and that there were alleged deficiencies in the PCR’s funding arrangements. The Tribunal rejected those objections, holding that, although the theory of harm was novel, the claim alleged class-wide loss arising from an overcharge and met the relevant certification standard. It further concluded that the claim was an apparently viable one with a good prospect of success.
Ben Lewy acted for Dr Stasi, instructed by Scott+Scott UK LLP.
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