| Shirley Road Management Company Limited | Households | 1982 |
| Shiv & Laxmi Limited | Wholesale & retail | 2024 |
| Shiv Ethnic Foods Limited | Wholesale & retail | 2020 |
| Shiv Food & Wine Limited | Wholesale & retail | 2024 |
| Shiv Mobile and Gadgets Solutions Limited | Wholesale & retail | 2021 |
| Shiv MOT Ltd | Wholesale & retail | 2024 |
| Shivshakti Estates Limited | Real estate | 2025 |
| Shkr Medical Limited | Health & social care | 2023 |
| Shlec Limited | Financial services | 2019 |
| Shoaib and Associates Limited | Health & social care | 2026 |
| Shoreline Maintenance Ltd | Construction | 2026 |
| Shoreside Property Developments Limited | Real estate | 2026 |
| Shoreview Technologies Ltd | Manufacturing | 2009 |
| Shotz Bar Ltd | Hospitality | 2023 |
| Showlight Ltd | Administrative & support | 2012 |
| SHR Land Limited | Financial services | 2024 |
| SHR Marlow Limited | Health & social care | 2018 |
| SHR Realinvestment Limited | Real estate | 2021 |
| Shrcompany Limited | Health & social care | 2016 |
| Shree RAM SAI Limited | Health & social care | 2023 |
| Shree Shyam and Shakti Ltd | Wholesale & retail | 2026 |
| Shri Gajanan Limited | Health & social care | 2016 |
| Shéa Beauty Organics Ltd | Wholesale & retail | 2018 |
| SIA House RTM Company Limited | Extraterritorial | 2024 |
| Sian Evans Inc Limited | Administrative & support | 2017 |
| Sicklebill Safaris Limited | Administrative & support | 2019 |
| Siddique Property Limited | Real estate | 2025 |
| Sidhu Sohal Ltd | Wholesale & retail | 2020 |
| Sidley Convenience Store Limited | Wholesale & retail | 2025 |
| Sidley Marion Holdings Limited | Financial services | 2020 |
| Siena Brooke Limited | Professional & scientific | 2015 |
| Sign Design (Sussex) Ltd | Manufacturing | 2018 |
| Signaserv Ltd | Administrative & support | 2011 |
| Signs Scott Limited | Manufacturing | 2009 |
| Signtek Commercial Ltd | Professional & scientific | 2025 |
| Silentrail Limited | Construction | 2017 |
| Silenus Beers Ltd | Wholesale & retail | 2021 |
| Silkra & Co Ltd | Real estate | 2006 |
| Silman Developments Limited | Real estate | 2022 |
| Silvatec Levels Limited | Extraterritorial | 2007 |
| Silver Business Holdings Limited | Financial services | 2021 |
| Silver II UK Holdings Limited | Professional & scientific | 2012 |
| Silver Moon Healing Ltd | Health & social care | 2019 |
| Silver Oak Realty Ltd | Hospitality | 2024 |
| Silver Property Lettings Limited | Real estate | 2020 |
| Silver Property Solutions Limited | Administrative & support | 2020 |
| Silver Transport Limited | Administrative & support | 2004 |
| Silver Wharf Estate Limited | Households | 2000 |
| Silver Wharf Management Limited | Households | 2000 |
| Silverbridge Ledger Ltd | Financial services | 2026 |
| Silverdale Lodge Residents Management Co Ltd | Households | 2012 |
| Silverdale Mews Residents Limited | Real estate | 2015 |
| Silverdale Tenants (Eastbourne) Limited | Households | 1976 |
| Silvered Skull Productions Ltd | Information & communication | 2021 |
| Silverhurst Limited | Households | 1995 |
| Silverline Secretaries Limited | Administrative & support | 2007 |
| Simes (Electrician) Limited | Construction | 2002 |
| Simmonds Decorating Contractors Limited | Construction | 2008 |
| Simmons Brothers (Seaford) Limited | Extraterritorial | 1959 |
| Simmons Roofing Limited | Construction | 2006 |
| Simon Abbott Limited | Wholesale & retail | 2004 |
| Simone Properties Ltd | Real estate | 2025 |
| Simonize Limited | Administrative & support | 2008 |
| Simpkins Associates Limited | Health & social care | 2021 |
| Simplantex Europe Limited | Wholesale & retail | 2020 |
| Simplantex Healthcare Limited | Manufacturing | 1992 |
| Simple EYE Surgery Ltd | Health & social care | 2022 |
| Simplify IT Limited | Information & communication | 2018 |
| Simply Bright (Brighton) Limited | Health & social care | 2025 |
| Simply Bright (Maidstone) Limited | Health & social care | 2012 |
| Simply Bright (Milton Regis) Limited | Health & social care | 2020 |
| Simply Bright (Mitcham) Limited | Health & social care | 2010 |
| Simply Bright Healthcare Limited | Financial services | 2010 |
| Simply Macro Strategy Limited | Financial services | 2017 |
| Simply MIS Ltd | Information & communication | 2023 |
| Simya Health Ltd | Health & social care | 2021 |
| Sinan's Medical Ltd | Health & social care | 2019 |
| Sinclair Swimming School Ltd | Education | 2016 |
| Singhs Fish Bar Limited | Hospitality | 2012 |
| Single Spark Ltd | Other services | 2019 |
| Singularity Creative Limited | Information & communication | 2015 |
| Sisu Health and Performance Limited | Health & social care | 2022 |
| SIX Dalton Road Residents Limited | Households | 2020 |
| SIX of Seven Ltd | Manufacturing | 2019 |
| SIX South Cliff Management Company Limited | Households | 2002 |
| Sixteen Fairfield Road (Eastbourne) Limited | Real estate | 1999 |
| Siya Health Limited | Health & social care | 2017 |
| SJ Moore Electrical Services Limited | Construction | 2015 |
| SJ Parmar Limited | Real estate | 2025 |
| SJB Capital Limited | Financial services | 2010 |
| SJD Consulting Solutions Ltd | Professional & scientific | 2025 |
| Sjdental Limited | Health & social care | 2020 |
| Sjdm Holdings Ltd | Financial services | 2024 |
| Sjlo Services Ltd | Professional & scientific | 2025 |
| SJS Plumbing & Heating Sussex Limited | Construction | 2018 |
| Skaterworld CIC | Arts & recreation | 2024 |
| Skeef Ltd | Hospitality | 2022 |
| Skender Ademi Limited | Hospitality | 2024 |
| Skfr Limited | Real estate | 2018 |
| SKG Dental Ltd | Health & social care | 2012 |