Thousands of UK businesses are being urged to come forward after a £2 billion collective legal action was launched against Microsoft, alleging that the tech giant overcharged customers who used its Windows Server software on rival cloud platforms such as Amazon Web Services (AWS), Google Cloud, and Alibaba Cloud.
The case, filed in the UK’s Competition Appeal Tribunal (CAT), has been brought by Dr Maria Luisa Stasi, a leading specialist in digital markets regulation. It seeks damages for businesses that, she says, have been forced to pay inflated prices due to Microsoft’s restrictive licensing practices.
“If your organisation has used Windows Server on Google, Amazon or Alibaba’s cloud platforms at any point since December 2018, you have likely paid too much money,” Dr Stasi said. “This legal action seeks to put that to an end.”
“Those responsible for IT or cloud contracting should get in touch. Billions have been drained from business budgets as a result of Microsoft’s licensing practices.”
Dr Stasi’s claim could become one of the largest antitrust lawsuits ever filed in the UK technology sector, potentially covering tens of thousands of organisations, from start-ups to multinationals.
The lawsuit closely follows the Competition and Markets Authority’s (CMA) final report on the UK’s cloud computing market, which concluded that Microsoft’s software licensing practices “adversely impact competition”.
The CMA found that Microsoft’s pricing model makes it more expensive for customers to run its software on rival clouds than on its own Azure service, effectively penalising businesses for using competitors’ infrastructure.
Those findings align directly with Dr Stasi’s case, which will return to court on 11 December 2025 for a hearing to decide whether it can proceed to full trial.
Legal experts say the case could set a precedent for collective actions against dominant technology firms accused of abusing market power in software and cloud services.
Cloud costs soar for UK businesses
The legal action comes amid mounting pressure on businesses struggling with escalating cloud costs.
Recent research shows that 67% of UK IT leaders expect their cloud expenses to rise further over the next year, with 68% of firms already cutting back in other IT areas to compensate.
Smaller organisations have been hit particularly hard. Many lack the resources to navigate complex licensing models or negotiate bespoke cloud contracts, leaving them vulnerable to hidden cost differentials.
“Cloud costs are soaring for UK businesses,” Dr Stasi said. “Getting in touch does not commit you to anything, but could result in your business clawing back a meaningful portion of its IT budget.”
The case against Microsoft is part of a wider wave of scrutiny directed at Big Tech’s control of the global cloud market.
Regulators across Europe, the US and Asia have intensified investigations into whether large technology firms are using software dominance to reinforce control over infrastructure markets.
In May 2025, the European Commission also signalled concern about “loyalty-inducing pricing” in cloud software licensing, echoing the CMA’s conclusions.
Microsoft has repeatedly defended its practices, saying its licensing models are “pro-competitive” and designed to “give customers choice and flexibility.”
If the CAT certifies Dr Stasi’s claim as a collective proceeding, affected organisations could automatically be included unless they opt out.
What happens next
A procedural hearing is scheduled for December 2025, after which the Tribunal will decide whether the case proceeds to trial. If successful, compensation could be distributed across all qualifying UK businesses that used Windows Server on rival clouds after December 2018.
Legal analysts say the potential £2 billion claim underscores the growing use of class-action-style competition litigation in the UK following Brexit, which allows domestic courts to take on global technology disputes previously handled in Brussels.
For now, businesses are being advised to register interest or provide usage data — a process that carries no obligation to join the claim but may determine eligibility for compensation later.
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£2bn UK lawsuit accuses Microsoft of overcharging cloud customers