The UK's Payments Systems Regulator (PSR) inadvertently cemented Mastercard and Visa's dominance in the British payments market, contrary to its stated goal of curbing banking oligopoly power. PSR aimed to foster competition by mandating banks share payment data and infrastructure, but industry consolidation and entrenched player advantages led to a stronger duopoly. This outcome leaves consumers facing higher fees and limited choice, while businesses grapple with inflexible processing systems. Mastercard and Visa now control over 90% of UK card transactions, raising regulatory scrutiny over interchange fees and network access.