Santander UK is a UK retail and commercial bank serving 13.6 million active customers. It operates as a ring-fenced bank — a regulatory structure that limits it to core retail and commercial banking activities — and is a wholly owned subsidiary of Banco Santander. The bank's dominant business is residential mortgage lending, which makes up 85% of its £197.4bn customer loan book. Santander UK lends primarily to owner-occupiers with prime credit quality, and to a lesser extent buy-to-let landlords. Beyond mortgages, the bank provides everyday retail banking products — current accounts, savings, credit cards, and unsecured loans — as well as banking services to small businesses. A smaller auto finance business (Santander Consumer UK) provides vehicle financing, and the corporate segment serves SMEs and mid-sized companies with loans, treasury, trade finance, and invoice finance. Santander UK earns money primarily through net interest income — the spread between loan rates and deposit costs — with NII representing over 90% of total operating income. The bank funds itself largely through retail deposits (£183.6bn) and uses a large structural hedge book to lock in yields on fixed-rate mortgage assets as deposit rates reprice. Santander UK sells to retail customers primarily through digital channels, supplemented by branches, and distributes mortgages both directly and via brokers. A notable pending deal: Banco Santander agreed in July 2025 to acquire TSB for approximately £2.65bn, which would add roughly £34bn in mortgages and bring the combined customer base to nearly 28 million, pending regulatory approval expected around Q2 2026.