| S.S.S.Gears Limited | Professional & scientific | 1950 |
| S.V.C.E. Limited | Information & communication | 1999 |
| S3KY Opportunities Limited | Real estate | 2017 |
| Saarc Limited | Information & communication | 2019 |
| Sabar Foods Ltd | Wholesale & retail | 2018 |
| Sabledene Limited | Administrative & support | 1985 |
| Sabor & CIA Ltd | Manufacturing | 2020 |
| Sabre Software Limited | Information & communication | 1996 |
| Sacet Ltd | Wholesale & retail | 2016 |
| Saeed Shop Ltd | Other services | 2018 |
| Safeabode Limited | Real estate | 2003 |
| Safeguard Security Oxford Ltd | Households | 2018 |
| Saferise Limited | Professional & scientific | 1988 |
| Sagoo & Takhar Limited | Real estate | 1976 |
| Sahota Enterprises Property Investment Limited | Real estate | 1997 |
| SAI Constructions Limited | Real estate | 1999 |
| SAI School of Harrow | Education | 1999 |
| Salaar Properties Limited | Real estate | 2006 |
| Salasji Limited | Wholesale & retail | 2003 |
| Salisbury Road (Harrow) Ltd | Real estate | 2007 |
| Sally Moore Limited | Arts & recreation | 2002 |
| Salon Sleek Limited | Other services | 2005 |
| Salter Electrical Limited | Construction | 2002 |
| Saltire Social Work Ltd | Health & social care | 2011 |
| Saltram Crescent Management Co. Limited | Households | 1999 |
| Salvia Flat Management Company Limited | Real estate | 1981 |
| Samantha Wear Ltd | Wholesale & retail | 2026 |
| Sami Limited | Construction | 2003 |
| Saminaya Limited | Real estate | 2003 |
| Sand and Aggregates Limited | Extraterritorial | 2001 |
| Sandhu Builders Maintenance Services Limited | Construction | 2005 |
| Sandwich Box Limited | Extraterritorial | 2006 |
| Sandy Lane (Northwood) Management Company Limited | Households | 1983 |
| Sandy Lodge Service Station Limited | Real estate | 1955 |
| Sangam Foundation | Health & social care | 2007 |
| Sanjay Investments Limited | Real estate | 2004 |
| Sanjivani Homes Ltd | Real estate | 2018 |
| Sanna (U.K.) Limited | Administrative & support | 1990 |
| Sans Consultants Ltd | Professional & scientific | 2004 |
| Sant Luxuries Ltd | Wholesale & retail | 2004 |
| Sanville Limited | | 1990 |
| Sapnay Limited | Arts & recreation | 2003 |
| Sapphire Real Estates Limited | Real estate | 2005 |
| Saracen Consultancy Limited | Information & communication | 2005 |
| Sarah Bussey Limited | Other services | 2015 |
| Sardes Limited | Wholesale & retail | 2001 |
| Sareko Limited | Professional & scientific | 2006 |
| Sarian Structures Limited | | 1976 |
| Saroj Limited | Construction | 2003 |
| Sash Media Limited | Information & communication | 1998 |
| Sasha KO Limited | Professional & scientific | 2005 |
| Satnam Builders Limited | Real estate | 1995 |
| Saturnalia UK Limited | Other services | 1992 |
| Saunders Holdings Limited | Extraterritorial | 1985 |
| Savile ROW Online Ltd | Wholesale & retail | 2022 |
| Savory Spice Ltd | Hospitality | 2018 |
| Saxeway Limited | Administrative & support | 1986 |
| Saynor Building Limited | Wholesale & retail | 1985 |
| SAZ IT & Freight Solutions Ltd | Transport & logistics | 2009 |
| SBK Finance Limited | Professional & scientific | 2023 |
| Sbs-Services Limited | Health & social care | 2006 |
| SC Blueprint Ltd | Information & communication | 2014 |
| Scadasys Technologies Limited | Professional & scientific | 2014 |
| Scan Corporation Limited | Real estate | 1990 |
| School of Experience Design Limited | Professional & scientific | 2020 |
| SCJ Contractor Services Limited | Professional & scientific | 2017 |
| Scott Crossley Construction Ltd | Construction | 2003 |
| Scott-Tech Limited | Construction | 2006 |
| Scotts Properties Limited | Real estate | 2002 |
| Screen-Tec Windscreens Limited | Wholesale & retail | 2007 |
| Scrumconnect Limited | Information & communication | 2011 |
| SD UK Properties Limited | Real estate | 2022 |
| SE London Development Ltd | Construction | 2017 |
| SE London Investment Ltd | Construction | 2021 |
| Sea Equals 8 Ltd | Financial services | 2022 |
| Sea Mills Property Limited | Real estate | 2007 |
| Seaforth Limited | | 1982 |
| Seagull Books London Limited | Information & communication | 2005 |
| Sealway Limited | Construction | 2005 |
| Sean ASH Limited | Information & communication | 2007 |
| Sears Dunbar Limited | Professional & scientific | 1998 |
| Seasons of Joy Children's Home Ltd | Health & social care | 2010 |
| Sectorlease Limited | Hospitality | 1990 |
| Secure by Design Limited | Professional & scientific | 1994 |
| Security Metal Works Limited | Manufacturing | 2003 |
| Security Response UK Limited | Administrative & support | 2008 |
| Sedass Limited | Information & communication | 1998 |
| Seddiqi Limited | Wholesale & retail | 2025 |
| Seema & Sona Builders Limited | Construction | 1978 |
| Seemeera Limited | Wholesale & retail | 2004 |
| Seerat Food and Wine Limited | Wholesale & retail | 2025 |
| Select Purchasing Limited | Wholesale & retail | 1992 |
| Select Toys Ltd | Hospitality | 2025 |
| Selectbase Limited | Other services | 1986 |
| Selective Foods Limited | Real estate | 1985 |
| Selekt Pizza Inn High Road Ltd | Hospitality | 2021 |
| Sellside Computing Limited | Professional & scientific | 1992 |
| Selvi Retail Ltd | Wholesale & retail | 2019 |
| Semu Limited | Health & social care | 2014 |
| Seniats Ltd | Real estate | 2017 |