| Sigtech Properties Limited | Real estate | 2019 |
| Sigtech Solutions Limited | Information & communication | 2013 |
| Sihra Properties Ltd | Real estate | 2025 |
| Sikdar Ltd | Real estate | 2021 |
| Sikh Temples R & S United KC Ltd Ltd | Arts & recreation | 2023 |
| Silchester Associates Ltd | Administrative & support | 2000 |
| Silks Property Investment Ltd | Real estate | 2021 |
| Silsonic Limited | Professional & scientific | 2007 |
| Silver Acquisition Co Limited | Professional & scientific | 2014 |
| Silver Project Solutions Ltd | Professional & scientific | 2025 |
| Silver Reece Ltd | Professional & scientific | 2018 |
| Silverfox Cybercloud IT Services Ltd | Information & communication | 2025 |
| Silverquest Limited | Wholesale & retail | 2010 |
| Sima Logistics Ltd | Transport & logistics | 2018 |
| Simison & Co Limited | Professional & scientific | 2007 |
| Simmons (Farnham) Ltd | Real estate | 2007 |
| Simon Clutterbuck Consultancy Services Limited | Professional & scientific | 2016 |
| Simon Dale Consulting Limited | Professional & scientific | 2021 |
| Simon Durrant Carpentry & Building Limited | Construction | 2005 |
| Simon Lyle Photography Ltd | Professional & scientific | 2016 |
| Simply Salt Ltd | Wholesale & retail | 2012 |
| Singh Nivesh Limited | Real estate | 2024 |
| Sinsible Food Ltd | Manufacturing | 2025 |
| SIR Battical Limited | Arts & recreation | 1991 |
| Siras Limited | Professional & scientific | 2026 |
| Siri Innovative Solutions Limited | Information & communication | 2014 |
| Sirius Coffee Limited | Manufacturing | 2023 |
| Siserone Limited | Information & communication | 1996 |
| Sisu Consultants Limited | Professional & scientific | 2015 |
| SIT Happens App Ltd | Information & communication | 2025 |
| Sita UK Limited | Extraterritorial | 1984 |
| Siteset Limited | Information & communication | 1995 |
| Sitestream Software Limited | Information & communication | 2013 |
| Sitting Pretty LDN Ltd | Manufacturing | 2024 |
| Sizzler Grill Limited | Hospitality | 2020 |
| Sizzler Maidenhead Limited | Hospitality | 2022 |
| Sizzlers Grill Ltd | Hospitality | 2025 |
| SJB Bourne Ltd | Administrative & support | 2017 |
| Sjbcadservices Ltd | Professional & scientific | 2019 |
| SJH Ltd | Professional & scientific | 2019 |
| SJL Driveways Limited | Construction | 2019 |
| SJM Group International Limited | Professional & scientific | 2024 |
| SJP 1 Limited | Financial services | 1980 |
| SK (Satgur Kirpa) Properties Ltd | Real estate | 2023 |
| SK Central Heating Services Ltd | Construction | 2022 |
| SK Insights Limited | Professional & scientific | 2017 |
| SK Manor Lane Limited | Real estate | 2022 |
| Skaab Holdings Ltd | Financial services | 2026 |
| Skad Assets Ltd | Real estate | 2021 |
| Skad Properties Ltd | Real estate | 2021 |
| Skad Real Estates Ltd | Real estate | 2020 |
| Skanda Choice Ltd | Wholesale & retail | 2025 |
| SKD Ahimah Limited | Professional & scientific | 2015 |
| Skellingtoons Ltd | Wholesale & retail | 2026 |
| SKG London Consulting Ltd | Information & communication | 2015 |
| Skgm Limited | Administrative & support | 2025 |
| Skill Forge Training Ltd | Education | 2025 |
| SKILL4CE Consultancy Limited | Information & communication | 2023 |
| Skin and Hair Aesthetics Ltd | Other services | 2022 |
| Skin NV Ltd | Health & social care | 2018 |
| Skin Revision Clinic Ltd | Health & social care | 2022 |
| Skin Sensations Limited | Other services | 2019 |
| Skip Hire National Limited | Water & waste | 2021 |
| SKM Oral Hygiene Limited | Health & social care | 2018 |
| SKS Property Holdings Limited | Real estate | 2019 |
| Sksk Solutions Ltd | Professional & scientific | 2013 |
| Skuber Limited | Information & communication | 2021 |
| Sky Brigade Consultancy Ltd | Administrative & support | 2017 |
| Skypacs Limited | Construction | 2024 |
| Skyridecarriage Ltd | Transport & logistics | 2024 |
| Skyseed Ltd | Information & communication | 2021 |
| SL 6 Limited | Financial services | 2006 |
| SL Auto Services Ltd | Manufacturing | 2011 |
| SL Farm Limited | Wholesale & retail | 2025 |
| SL PAY Index Ltd | Wholesale & retail | 2023 |
| SL PHC Limited | Financial services | 2025 |
| SL6 Appliances Limited | Administrative & support | 2009 |
| SL6 Consulting Ltd | Information & communication | 2012 |
| SL6 Investments Limited | Extraterritorial | 2010 |
| SL6 Marketing Limited | Professional & scientific | 2016 |
| SL6 Property (Camden) Limited | Real estate | 2025 |
| Slade Glass Limited | Construction | 1995 |
| Slapbars Limited | Hospitality | 2025 |
| SLC International Private Limited | Wholesale & retail | 2021 |
| Sleek Aesthetics Ltd | Other services | 2022 |
| Sleep 8 Intrinsic Limited | Wholesale & retail | 2022 |
| Slotcount Limited | Professional & scientific | 1990 |
| Slough Philharmonic Productions Limited | Arts & recreation | 2017 |
| Slowe Living Ltd | Manufacturing | 2021 |
| Slowstream Property Management Limited | Households | 1985 |
| SLS Landscaping Ltd | Construction | 2020 |
| SMA Specialists Ltd | Administrative & support | 2017 |
| Small Lots (Mix-It) Limited | Professional & scientific | 1984 |
| Small Screen Science Ltd | Information & communication | 2013 |
| Smalloak Limited | Real estate | 2016 |
| Smalltech Solutions Ltd | Professional & scientific | 2009 |
| Smart Build and Interiors Limited | Administrative & support | 2024 |
| Smart Realty Ltd | Real estate | 2021 |
| Smart Space Design & Development Ltd | Construction | 2014 |
| Smart Wheels (Southern) Limited | Wholesale & retail | 2011 |