| Simon's Retail Group Ltd | Wholesale & retail | 2025 |
| Simply Business Finance Limited | Financial services | 2017 |
| Simply Business Loans Limited | Financial services | 2019 |
| Simply Cleaning Sussex Ltd | Administrative & support | 2011 |
| Simplyvat Limited | Administrative & support | 2025 |
| Simsbury Limited | Professional & scientific | 2024 |
| Simulation Ride Limited | Information & communication | 2022 |
| SIN Network Ltd | Wholesale & retail | 2018 |
| Sinclair Homes Group Ltd | Real estate | 2025 |
| Sindens Limited | Construction | 1997 |
| Singa Ltd | Financial services | 2024 |
| Singing Hills Ltd | Financial services | 2019 |
| SIP Neat Ltd | Wholesale & retail | 2024 |
| Sippclub Ltd | Administrative & support | 2012 |
| Sirin Properties Limited | Real estate | 2019 |
| Sironko Group Limited | Households | 2025 |
| SIX Cylinder Limited | Professional & scientific | 2012 |
| SIX Second Avenue Management Company Limited | Households | 1958 |
| Sixfingers Limited | Information & communication | 2015 |
| SJ Transport Limited | Other services | 2019 |
| Sjdc Dental Limited | Health & social care | 2022 |
| SJF Estates Limited | Real estate | 2006 |
| SJK Orthodontics Ltd | Health & social care | 2025 |
| SJL Dental Studios Ltd | Health & social care | 2009 |
| Sjpl Group Ltd | Health & social care | 2021 |
| SJR Endo Limited | Health & social care | 2020 |
| SJW Events Ltd | Administrative & support | 2015 |
| Skandar Property Ltd | Real estate | 2025 |
| Skerritt Financial Planning Ltd | Professional & scientific | 2026 |
| Skezza Ltd | Professional & scientific | 2023 |
| Skillbridge Advisors Ltd | Professional & scientific | 2025 |
| Skillsmart Ltd | Administrative & support | 2022 |
| Skin and Pulp Ltd | Hospitality | 2018 |
| Skin Associates (Holdings) Limited | Administrative & support | 2013 |
| Skin Associates (Medical) Limited | Administrative & support | 2013 |
| Skin Associates Limited | Health & social care | 2012 |
| Skinlight Cosmetics Limited | Wholesale & retail | 2004 |
| Skinner Brothers Music Ltd | Information & communication | 2020 |
| Sky Diagnostics Limited | Health & social care | 2024 |
| Sky Team Ltd | Construction | 2018 |
| Skyecap Ltd | Financial services | 2023 |
| Skyface Ltd | Transport & logistics | 2021 |
| Skylark Promotions Limited | Other services | 2020 |
| Skylight Arts Limited | Arts & recreation | 2014 |
| Skyworks Solutions Limited | Manufacturing | 2002 |
| Skülptur Limited | Education | 2023 |
| Slabstock Holdings Ltd | Real estate | 2025 |
| Slabstock Ltd | Real estate | 2025 |
| Slasco Developments Ltd | Construction | 2023 |
| Slasco Holdings Ltd | Financial services | 2024 |
| Slasco Investments Ltd | Real estate | 2024 |
| Slasco Properties Ltd | Construction | 2024 |
| Slasco Property Investments Ltd | Real estate | 2026 |
| Slaughterhouse Publishing Limited | Information & communication | 2025 |
| Slaven and Jones Ltd | Extraterritorial | 2013 |
| SLM People Solutions Limited | Administrative & support | 2025 |
| SLN Capital Holdings Limited | Financial services | 2025 |
| SLP Utilities Ltd | Administrative & support | 2021 |
| SLS Legal Limited | Professional & scientific | 2009 |
| SM Class Properties Limited | Real estate | 2024 |
| Small Cat Investments Limited | Financial services | 2024 |
| Small JOB Plumbers Ltd | Construction | 2013 |
| Smart Approve Ltd | Information & communication | 2019 |
| Smart Commercial Vehicles Ltd | Wholesale & retail | 2021 |
| Smart Developments Sussex Limited | Construction | 2013 |
| Smart Group Enterprises Limited | Wholesale & retail | 2013 |
| Smart NMN Limited | Wholesale & retail | 2024 |
| Smart Site Services Limited | Construction | 2024 |
| Smarthelpai Ltd | Information & communication | 2025 |
| Smashing Books Ltd | Arts & recreation | 2003 |
| Smikle Dance Studio Ltd | Education | 2023 |
| Smile Holidays Ltd | Administrative & support | 2006 |
| Smileone Pimlico Ltd | Health & social care | 2023 |
| Smiles by Sanj Limited | Health & social care | 2023 |
| Smiling Staff Ltd | Administrative & support | 2019 |
| Smith & Co Galleries Ltd | Arts & recreation | 2019 |
| Smith Marketing Ltd | Wholesale & retail | 2024 |
| Smith United Limited | Arts & recreation | 2000 |
| Smithdales Limited | Extraterritorial | 2011 |
| Smithwood C J Limited | Manufacturing | 2014 |
| Smizma Limited | Health & social care | 2011 |
| SMK Ventures Ltd | Information & communication | 2026 |
| Smmc Holdings (Sussex) Limited | Financial services | 2022 |
| Smokey JOE BBQ Ltd | Hospitality | 2024 |
| Smugglers Mews Residents Company Limited | Households | 2018 |
| Snap Finger Click Limited | Information & communication | 2015 |
| Snap Kitchens Ltd | Hospitality | 2017 |
| Snape Property Investments Ltd | Real estate | 2024 |
| SNE Consulting Ltd | Information & communication | 2007 |
| Snoek Group Ltd | Wholesale & retail | 2023 |
| Snog Limited | Professional & scientific | 1999 |
| Snow Camp | Health & social care | 2003 |
| Snow Shakes Ltd | Hospitality | 2018 |
| Snowline Ice Cream Limited | | 1982 |
| Snowy Beauty Ltd | Other services | 2024 |
| SO Business Consultants Limited | Administrative & support | 2020 |
| SO Well Together Ltd | Public administration | 2024 |
| Soaked Cosmetics Ltd | Wholesale & retail | 2019 |
| Soar Consultancy Services Limited | Professional & scientific | 2016 |
| Social Science Ltd | Professional & scientific | 2025 |