Britain Adds Amazon to the Platform Liability Ledger

On 13 October 2026 the Competition Appeal Tribunal issued [2026] CAT 77, conditionally certifying opt-out collective proceedings brought by the Association of Consumer Support Organisations (ACSO) against Amazon group defendants. ACSO alleges that price parity policies applied to third-party sellers on Amazon’s UK marketplace infringed Chapter I and Chapter II of the Competition Act 1998—and, for conduct before 31 December 2020, Articles 101 and 102 of the Treaty on the Functioning of the European Union. Certification is a procedural gate: it authorises a class representative and shapes how experts and funding must align. It is not a finding that Amazon broke the law.

The timing matters. On 9 October the same tribunal published reasons approving a £260 million collective settlement in Professor Barry Rodger’s Play Store damages case against Google—Britain’s highest-value CAT settlement to date, as we reported in Britain’s Google fight now has a price tag. Amazon’s ruling does not settle anything. It adds a third damages vehicle to a docket that was already moving toward trial.

Three claims, one calendar

Amazon is not facing a single novel lawsuit. The tribunal had already granted collective proceedings orders in two related actions: Robert Hammond on behalf of consumers and Professor Andreas Stephan on behalf of merchants, both alleging abuse of dominance under Chapter II (and pre-Brexit Article 102). Those matters are jointly case-managed with ACSO’s price-parity claim. A joint stage 1 trial is listed to start on 25 April 2028 on market definition, dominance, and liability; a stage 2 trial would follow on causation, overcharge, and pass-on.

ACSO filed its application on 14 August 2025. After a hearing on 5–6 October 2026, the tribunal said it would authorise ACSO as class representative provided fee caps (£150 per hour, £750 daily), a revised litigation budget, and amendments to the litigation funding agreement are filed within four weeks. Certification will be opt-out. Expert evidence must be coordinated with Hammond and Stephan: for trial 1, ACSO is to share Dr Pike and Hammond’s counsel on market definition and dominance, and to align with Stephan’s team on liability economics—reflecting the tribunal’s view that ACSO’s initial expert methodology on price-parity effect did not meet the Microsoft test and that duplicate experts would be disproportionate.

For readers tracking platform power in Brussels, the parallel is structural rather than doctrinal. EU gatekeeper designations and DMA conduct duties still turn on adjacency and leverage (Brussels defining platform power by adjacency); Britain’s CAT track turns alleged marketplace rules into quantifiable collective exposure whether or not Amazon sits in a formal gatekeeper list (why Brussels spared edge from DMA gatekeeper status). Compliance with a regulator’s forward-looking remedy does not automatically cap retrospective damages in the UK model.

Certification is not conviction

Headlines that treat [2026] CAT 77 as “Amazon loses” misread the instrument. The tribunal explicitly reserved fuller reasons for a later judgment, including Amazon’s application for summary judgment or strike-out on the Chapter I limb. ACSO must confirm within four weeks whether it will proceed on the tribunal’s terms. Even after trial 1, ACSO may need a revised expert methodology to prove causation and quantum at trial 2—or fall back to shared experts with Hammond and Stephan.

That procedural thickness is the story. Britain is building a private enforcement layer on top of competition law: opt-out classes, litigation funders, and multi-year trial schedules that keep marketplace conduct on the balance sheet as contingent liability rather than as a one-off regulatory fine. Google’s settlement showed the exit ramp—cash for class members and funders when risk and duration justify a deal. Amazon’s certification shows the entry ramp—another major platform operator on the same ledger while liability remains contested.

Price parity, in competition terms, is the requirement that sellers not offer lower prices on other channels. ACSO’s claim ties consumer harm to those rules on the UK marketplace. Stephan’s merchant class alleges dominance abuse in overlapping conduct. Hammond’s consumer action shares the same trial architecture. Case management conferences scheduled for 14 October 2026 (with a reserve day) were the immediate reason the tribunal issued CAT 77 on an urgent basis before fuller reasons land.

What to watch

ACSO’s four-week election. Revised budget and funding terms determine whether the conditional certification hardens into a live third claim.

Joint trial 1 (April 2028). Market definition and dominance findings would bind the shape of all three actions; liability on price parity and merchant abuse is fought once, not three times.

Chapter I strike-out motion. If Amazon succeeds on summary judgment for the cartel limb, ACSO’s narrative narrows to dominance and parity mechanics already central to Stephan.

Settlement politics. Rodger’s Google deal does not predict Amazon’s posture—Amazon is years from trial 2 quantum—but it establishes that UK collective proceedings can monetise platform terms at nine-figure scale when defendants prefer certainty.

Britain’s platform regime is no longer only about what regulators will let operators do next quarter. It is also about whether past marketplace pricing rules can ride collective damages all the way to a numbered trial date—and, for Amazon, that date is now on the public calendar.