| Specialist Insurance Solutions Limited | Financial services | 1999 |
| Speclar Ltd | Administrative & support | 2009 |
| Spectrum Security & Fire Limited | Administrative & support | 1997 |
| Spenser and Forshaw Limited | Financial services | 2024 |
| SPH Builders (Southern) Limited | Construction | 2019 |
| Spice Islands Friends Ltd | Arts & recreation | 2019 |
| Spike Ecology Ltd | Professional & scientific | 2026 |
| Spindles Concrete Pumping Limited | Construction | 2019 |
| Spintech Engineering Ltd | Professional & scientific | 2026 |
| Spire View Properties Limited | Real estate | 2016 |
| Spitfire Alarm & Electrical Limited | Construction | 2015 |
| Spitfire Railtours Ltd | Administrative & support | 2007 |
| Spitfire Taekwondo Eastleigh Limited | Arts & recreation | 2026 |
| Splash Abacus Ltd | Energy | 2017 |
| Splashmaps Ltd | Information & communication | 2012 |
| Sporia Sports Ltd | Arts & recreation | 2022 |
| Sport 2 Aspire Limited | Education | 2024 |
| Sport in the Community 2020 CIC | Education | 2020 |
| Sporting Journeys Ltd | Administrative & support | 1996 |
| Spot on Developments Limited | Hospitality | 2007 |
| Spray Coatings Limited | Construction | 2015 |
| Spraytech (Southern) Limited | Construction | 2008 |
| Spring Care & Health Ltd | Extraterritorial | 1998 |
| Springbanks Medical Limited | Health & social care | 2017 |
| Springbanks Properties Limited | Real estate | 2020 |
| Springboard Business Services Ltd | Administrative & support | 2022 |
| Springboard Employment & Training Group | Education | 1997 |
| Springhill Farms (Southern) Limited | Real estate | 2025 |
| Springhill Plant Ltd | Wholesale & retail | 2023 |
| Sprint IT Solutions Limited | Information & communication | 2012 |
| Sprint Rentals Limited | Real estate | 2023 |
| Spruce Town Planning Ltd | Professional & scientific | 2019 |
| SPS (South) Ltd | Construction | 2014 |
| SPS Southern Limited | Transport & logistics | 2019 |
| Squadz Ltd | Information & communication | 2025 |
| Square Group Investments Ltd | Real estate | 2025 |
| Square Group Lettings Ltd | Real estate | 2025 |
| Square Group Ltd | Financial services | 2025 |
| Square One Construction Limited | Construction | 2009 |
| SRI Vinayak Consultancy Limited | Information & communication | 2021 |
| SRI Vinayak Properties Limited | Real estate | 2024 |
| Srinya Ltd | Health & social care | 2019 |
| SRJ Plumbing and Heating Limited | Construction | 2023 |
| SRL (UK) Property Limited | Real estate | 2022 |
| SS Site Engineering Ltd | Construction | 2021 |
| SS Tricky Lifting Services Ltd | Administrative & support | 2024 |
| SSD Centaur Limited | Wholesale & retail | 2022 |
| SSN Enterprises Limited | Hospitality | 2011 |
| Ssng Properties Ltd | Real estate | 2022 |
| ST Denys Court RTM Company Ltd | Households | 2018 |
| ST. Cross Electronics Limited | Manufacturing | 1984 |
| St.Clare Engineering Limited | Manufacturing | 1959 |
| Stackpole Property Limited | Real estate | 2018 |
| Stanford Estate Agents Limited | Real estate | 2012 |
| Stanford Mortgage & Financial Services Limited | Financial services | 2015 |
| Stanmore Houses Limited | Real estate | 2018 |
| Stanmore Lettings Limited | Real estate | 2012 |
| Stanmore Shops Limited | Wholesale & retail | 2007 |
| Stanmore Stores Ltd | Wholesale & retail | 2012 |
| Stanshield Engineering Limited | Manufacturing | 1997 |
| Stantay Design Innovations Limited | Professional & scientific | 1994 |
| Star Care Agency Limited | Administrative & support | 2016 |
| Starblue Properties Ltd | Real estate | 2024 |
| Starburst Boutique Limited | Wholesale & retail | 2008 |
| Starfizz Words and Learning Limited | Professional & scientific | 2011 |
| Starry Night Environmental Technology Co., Ltd | Wholesale & retail | 2026 |
| Starshape Games Limited | Information & communication | 2013 |
| State 5 Driver Training Ltd | Education | 2019 |
| Staylane Media Ltd | Information & communication | 2021 |
| STC Southern Ltd | Construction | 2023 |
| Stealth Building Services Ltd | Construction | 2023 |
| Steam Shower Supplies T/A Steamist Limited | Wholesale & retail | 1997 |
| Steam Town Brewco Limited | Manufacturing | 2017 |
| Steam Town Pubco Limited | Hospitality | 2023 |
| Steele Creative Limited | Wholesale & retail | 2017 |
| Stellamartinstec Limited | Administrative & support | 2022 |
| Stellar Spectra Ltd | Information & communication | 2019 |
| Stellaroptics Limited | Manufacturing | 2024 |
| Stephanie Atkins Photography Ltd | Professional & scientific | 2024 |
| Stephen Field Associates Ltd | Professional & scientific | 2009 |
| Stephen Jayne Publications Ltd | Manufacturing | 2006 |
| Stephen Moore Innovation Limited | Professional & scientific | 2021 |
| Stephen Price Surveyor Limited | Professional & scientific | 2018 |
| Stesh Cleaning Solutions Limited | Administrative & support | 2021 |
| Steve Pothecary Agencies Limited | Wholesale & retail | 2015 |
| Steve Thomas Consultancy Limited | Professional & scientific | 2011 |
| Stevens Marine Limited | Professional & scientific | 2013 |
| Steventon Assets Limited | Real estate | 2015 |
| Steward & Keel Ltd | Professional & scientific | 2026 |
| Stewart Signs Holdings Limited | Financial services | 2016 |
| Stingo Ltd | Information & communication | 2013 |
| Stockley Mortgage and Protection Ltd | Financial services | 2026 |
| Stoddart and Stone Technology Ltd | Information & communication | 2025 |
| Stoic Media Ltd | Information & communication | 2021 |
| Stoke Common Road Ltd | Households | 2021 |
| Stokewood Recruitment Services Ltd | Administrative & support | 2024 |
| Stomper Events Ltd | Arts & recreation | 2022 |
| Stone Circle South Ltd | Real estate | 2017 |
| Stone Consulting Engineers Limited | Construction | 2003 |
| Stone Osmond Accountants Ltd | Professional & scientific | 2019 |