| Simone Michelle the Hair Salon Limited | Other services | 2025 |
| Simply TRA Limited | Wholesale & retail | 2010 |
| Sinanal Ltd | Hospitality | 2019 |
| Sirbob Holdings Limited | Financial services | 2021 |
| SJS Freight Ltd | Transport & logistics | 2011 |
| SJS Marketing Ltd | Professional & scientific | 2007 |
| Skycloseups Limited | Information & communication | 2020 |
| Skyline Window Cleaning (EA) Ltd | Real estate | 2019 |
| SLF Products Ltd | Wholesale & retail | 2022 |
| Small Copper Ltd | Construction | 2018 |
| Small Room Empire Limited | Information & communication | 2025 |
| Smart Network Development Ltd | Transport & logistics | 2024 |
| SMC Marketing Ltd | Administrative & support | 2021 |
| Smeets Ferry UK Ltd | Transport & logistics | 2014 |
| Smeets Transport UK Ltd | Transport & logistics | 2016 |
| SMK Smart Transport Ltd | Transport & logistics | 2025 |
| Smoke Control Training Ltd | Education | 2021 |
| SMS Transport Ltd | Transport & logistics | 2018 |
| Smsm Limited | Transport & logistics | 2024 |
| Smudge Holdco Ltd | Financial services | 2021 |
| Solutions E2 Ltd | Professional & scientific | 2016 |
| Sorinionitauk Ltd | Wholesale & retail | 2019 |
| South Atlantic Container Line Limited | Extraterritorial | 2016 |
| Spa Pavilion Limited | Arts & recreation | 2015 |
| Spa Pavilion Productions Limited | Hospitality | 2016 |
| Sparkling Consultants Limited | Administrative & support | 2025 |
| Spider Web Art Ltd | Arts & recreation | 2018 |
| Spiritz International Ltd | Wholesale & retail | 2024 |
| Splitbark Studio Ltd | Manufacturing | 2023 |
| Spzp Limited | Real estate | 2024 |
| SS & AS Trading Ltd | Other services | 2023 |
| SSL Medical Limited | Health & social care | 2026 |
| SSL Security Services Limited | Administrative & support | 2022 |
| ST Andrews Pre-School Limited | Education | 2013 |
| Stag Land Rover Ltd | Wholesale & retail | 2019 |
| Starfuse Ltd | Information & communication | 2014 |
| Steamboat Creative Ltd | Arts & recreation | 2016 |
| Steel River Films Ltd | Information & communication | 2018 |
| Step Forward Education Limited | Education | 2020 |
| Stepmum Space Ltd | Other services | 2025 |
| Steve Atkinson Plumbing & Heating Limited | Construction | 2014 |
| Sticar-It Limited | Information & communication | 2013 |
| Stomanns Developments Ltd | Administrative & support | 2017 |
| Stop Shop Felixstowe Ltd | Wholesale & retail | 2026 |
| STUDIO8 Felixstowe Limited | Real estate | 2016 |
| Sturmans Decorating Ltd | Construction | 2022 |
| Stylish Furniture EN Ltd | Wholesale & retail | 2016 |
| Suffolk at Play Ltd | Education | 2020 |
| Suffolk Automotive Ltd | Wholesale & retail | 2024 |
| Suffolk Coastal Construction Limited | Construction | 2025 |
| Suffolk Community Scrapstore CIC | Wholesale & retail | 2024 |
| Suffolk Hot TUB Hire Ltd | Administrative & support | 2016 |
| Suffolk Hot Tubs Ltd | Administrative & support | 2016 |
| Suffolk Ladies County Golf Association Limited | Arts & recreation | 2023 |
| Suffolk Ladies Fitness Limited | Arts & recreation | 2011 |
| Suffolk Landscaping Services Limited | Administrative & support | 2017 |
| Suffolk Mind | Health & social care | 1991 |
| Suffolk Mind (Trading) Ltd | Extraterritorial | 1996 |
| Suffolk Repointing Specialists Ltd | Construction | 2024 |
| Suffolk Stone Limited | Construction | 2022 |
| Summit Ventures Limited | Health & social care | 2020 |
| Sy's Auto Detailing Ltd | Manufacturing | 2025 |
| Szallito Transport Ltd | Transport & logistics | 2018 |
| T Baker Holdings Ltd | Financial services | 2023 |
| T27 Hair Ltd | Other services | 2022 |
| Tamuka Ltd | Information & communication | 2007 |
| Tandem Global Logistics Limited | Professional & scientific | 2007 |
| Task Transport Ltd | Transport & logistics | 2024 |
| Tax Britannia Limited | Information & communication | 1995 |
| TBT & Sons Limited | Transport & logistics | 2023 |
| TC Transport Ltd | Transport & logistics | 2023 |
| TCN Transport Ltd | Transport & logistics | 2023 |
| Tea and Kate Ltd | Wholesale & retail | 2013 |
| Techco Ltd | Wholesale & retail | 2024 |
| TEO & SI Limited | Transport & logistics | 2017 |
| Tercha Ltd | Real estate | 2023 |
| TES Holding Group Limited | Financial services | 2022 |
| Thamesport (London) Limited | Transport & logistics | 1987 |
| THE 121 Clinic Ltd | Other services | 2025 |
| THE Alfa Romeo Owners Club Limited | Other services | 1973 |
| THE Bar District Ltd | Hospitality | 2024 |
| THE Cedar Room Ltd | Construction | 2013 |
| THE Cellar Bar (Felixstowe) Limited | Hospitality | 2025 |
| THE Dene Management Limited | Real estate | 1987 |
| THE Falcon Inn Felixstowe Ltd | Hospitality | 2025 |
| THE Falcon Inn Limited | Hospitality | 2021 |
| THE Felixstowe Directory Limited | Information & communication | 2010 |
| THE Felixstowe Dock and Railway Company | Transport & logistics | 1875 |
| THE Felixstowe Flyer Limited | Professional & scientific | 2010 |
| THE Felsto Arms Ltd | Hospitality | 2010 |
| THE Financial Performance Company Ltd | Professional & scientific | 2011 |
| THE Foot Healthcare Centre Limited | Health & social care | 2005 |
| THE G M Building (Ipswich) Residents Management Limited | Households | 2018 |
| THE Garden LOU Ltd | Administrative & support | 2021 |
| THE Greenways Partnership Limited | Professional & scientific | 1993 |
| THE Haven (Felixstowe) Limited | Households | 1999 |
| THE Health & Fitness Coach Ltd | Health & social care | 2022 |
| THE Little Cheese Company Ltd | Wholesale & retail | 2022 |
| THE Little Desk Co. Ltd | Wholesale & retail | 2021 |
| THE Little Wine Bar Company Ltd | Hospitality | 2021 |