- Santander - Macclesfield
- Santander - Magherafelt
- Santander - Maidenhead
- Santander - Maidstone
- Santander - Maldon
- Santander - Malvern
- Santander - Manchester, 130, Market Street, Piccadilly Gardens
- Santander - Manchester, 28/34, Cross Street
- Santander - Mansfield, 52-54, Westgate
- Santander - Mansfield, 9, Stockwell Gate
- Santander - March
- Santander - Margate
- Santander - Market Harborough
- Santander - Marlow
- Santander - Melton Mowbray
- Santander - Merthyr Tydfil
- Santander - Middlesbrough, 17/19, Linthorpe Road
- Santander - Middlesbrough, 69, Linthorpe Road
- Santander - Middleton, 16, Middleton Gardens
- Santander - Middleton, Colmar House, Manchester New Road
- Santander - Mill Hill
- Santander - Milngavie
- Santander - Milton Keynes, 201, Grafton Gate East
- Santander - Milton Keynes, 29, Midsummer Place
- Santander - Milton Keynes, 695-697 Silbury Boulevard
- Santander - Minehead
- Santander - Mold
- Santander - Monmouth
- Santander - Moorgate
- Santander - Morden
- Santander - Morecambe
- Santander - Moreton
- Santander - Morley
- Santander - Morpeth
- Santander - Musselburgh
- Santander - Muswell Hill