DEPOSITS BY CUSTOMERS (Details) - GBP (£) £ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Disclosure Of Deposits From Customers [Line Items] | ||
| Deposits by customers | £ 224,589 | £ 187,300 |
| Demand and time deposits | ||
| Disclosure Of Deposits From Customers [Line Items] | ||
| Deposits by customers | 221,839 | 184,155 |
| Amounts due to other Santander UK Group Holdings plc subsidiaries | ||
| Disclosure Of Deposits From Customers [Line Items] | ||
| Deposits by customers | 186 | 182 |
| Amounts due to Santander UK Group Holdings plc | ||
| Disclosure Of Deposits From Customers [Line Items] | ||
| Deposits by customers | 843 | 1,373 |
| Amounts due to fellow Banco Santander subsidiaries and joint ventures | ||
| Disclosure Of Deposits From Customers [Line Items] | ||
| Deposits by customers | 1,721 | 1,590 |
| Equity index linked deposits | ||
| Disclosure Of Deposits From Customers [Line Items] | ||
| Capital amount guaranteed or protected | £ 69 | £ 87 |