| Sigma Software Limited | Information & communication | 2015 |
| Silver BEE Bakery Limited | Manufacturing | 2008 |
| Silver Bough Limited | Mining & quarrying | 2016 |
| Silverlight Care Limited | Health & social care | 2014 |
| Silverstag Creative Limited | Professional & scientific | 2012 |
| Simon Turner Refrigeration Limited | Administrative & support | 2018 |
| Simple Beast Limited | Information & communication | 2020 |
| Sinclaire Property Services Ltd | Administrative & support | 2020 |
| Sine Construction Services Limited | Professional & scientific | 2010 |
| Sippi Limited | Other services | 2022 |
| Sirona Ltd | Professional & scientific | 2018 |
| Siskin Property Ltd | Real estate | 2012 |
| Siskin Property Management Ltd | Real estate | 2018 |
| Sisters and Seasons Ltd | Real estate | 2018 |
| SIX West Strategy Consulting Limited | Professional & scientific | 2018 |
| SJ Pickup and Co Ltd | Professional & scientific | 2007 |
| Sk:Nfusion Ltd | Health & social care | 2023 |
| Skills and Trades Ltd | Administrative & support | 2024 |
| SKS Windows Limited | Construction | 2009 |
| Skyra House Ltd | Wholesale & retail | 2026 |
| SLB Estates Ltd | Real estate | 2017 |
| Slinco Ltd | Wholesale & retail | 2019 |
| Sliver of Light Ltd | Wholesale & retail | 2021 |
| Smart Choice Minibus Services Ltd | Transport & logistics | 2025 |
| Smart People Hub Ltd | Professional & scientific | 2025 |
| Smarte Trading Ltd | Wholesale & retail | 2011 |
| Smartlix Ltd | Information & communication | 2020 |
| Smartwood Limited | Extraterritorial | 2003 |
| Smokin Crust Limited | Hospitality | 2024 |
| SMR76 Ltd | Real estate | 2025 |
| SMR77 Ltd | Real estate | 2022 |
| Smtb Limited | Other services | 2025 |
| SMV Training Limited | Education | 2021 |
| SND Carpentry Limited | Construction | 2016 |
| Sobacm Ltd | Information & communication | 2015 |
| Soccer Mambo Ltd | Arts & recreation | 2022 |
| Social Bubble Pods Ltd | Wholesale & retail | 2020 |
| Social Phoenix Limited | Real estate | 2020 |
| Solopreneur International Ltd | Information & communication | 2025 |
| Sophie Griffiths Ltd | Professional & scientific | 2022 |
| Sophlan Consulting Limited | Information & communication | 2013 |
| Sorted by Design Ltd | Other services | 2024 |
| Sorted WS Ltd | Manufacturing | 2022 |
| South Coast Conventions Limited | Arts & recreation | 2012 |
| South Coast Systems Limited | Manufacturing | 2003 |
| South Downs Venison, Game (and Fungi) Ltd | Agriculture & fishing | 2026 |
| South East Driveways Ltd | Construction | 2020 |
| South East Health & Safety Limited | Other services | 2006 |
| South Phase Electrical Ltd | Construction | 2023 |
| South Street Spice Ltd | Hospitality | 2025 |
| Southbourne Accountancy Limited | Professional & scientific | 2022 |
| Southdown Aviation Services Ltd | Education | 2019 |
| Southeast Communities Rail Partnership CIC | Transport & logistics | 2008 |
| Southeast Print & Signs Limited | Professional & scientific | 2013 |
| Southern Commercial Laundry Services Limited | Manufacturing | 2015 |
| Southern Counties Window Cleaning Limited | Administrative & support | 2011 |
| Southern Motors Ltd | Construction | 2019 |
| Southrend Ltd | Construction | 2021 |
| Sovereign Cargo Limited | Transport & logistics | 1999 |
| Sovereign Certification Limited | Professional & scientific | 2004 |
| Sovereign Shading Systems Ltd | Construction | 2022 |
| Spabox Limited | Wholesale & retail | 2009 |
| Spacelinkpros Ltd | Information & communication | 2022 |
| Spalding Enterprises Limited | Construction | 2012 |
| Sparc PM Ltd | Other services | 2017 |
| Sparkk Investments Limited | Real estate | 2019 |
| Spearpoint Consultants Limited | Financial services | 2018 |
| Spearpoint Estate Planners Ltd | Financial services | 2018 |
| Speedbird Offshore Yacht Club Limited | Transport & logistics | 2005 |
| Speksa Limited | Professional & scientific | 2016 |
| Spencer Road Management Company Limited | Households | 1970 |
| Spirit Horse Ltd | Health & social care | 2026 |
| Sport Arabia Limited | Arts & recreation | 2007 |
| Spray Granite Services Ltd | Administrative & support | 2023 |
| Springwood Enterprises Limited | Education | 2011 |
| Sprout Accounting Ltd | Administrative & support | 2017 |
| SQL Deployment Cloud Ltd | Information & communication | 2018 |
| SSC Brighton Limited | Education | 2021 |
| ST James Heights RTM Company Limited | Real estate | 2014 |
| ST. Anne's Eastbourne Residents Association Limited | Households | 1970 |
| ST. Denys Residents Association Limited | Households | 1970 |
| Star Brighton Ltd | Real estate | 2025 |
| Star Fuels South East Ltd | Construction | 2020 |
| STC Motors Ltd | Wholesale & retail | 2003 |
| Steeple Grange Management (Eastbourne) Limited | Households | 1985 |
| Stegro Verwaltungs Ltd Ltd. | Wholesale & retail | 2026 |
| Stephen Bartlett Studio Limited | Arts & recreation | 2002 |
| Sterling March Ltd | Extraterritorial | 2013 |
| Stonebusters Ltd | Health & social care | 2011 |
| Streat Greek Ltd | Hospitality | 2021 |
| Stud Farm Residents Limited | Households | 2001 |
| Studio Felix Ltd | Professional & scientific | 2014 |
| Studio Sett Ltd | Professional & scientific | 2025 |
| Studio Tans Limited | Other services | 2011 |
| Stulane.Com Limited | Information & communication | 2019 |
| Sturdy Joinery and Shopfitting Ltd | Construction | 2019 |
| SUE and Charlie Limited | Hospitality | 2026 |
| Suffolk Community Energy CIC | Energy | 2022 |
| Sugar Rush to YOU Limited | Hospitality | 2018 |
| Sumi.Makeover Ltd | Other services | 2024 |