| Sireen House Limited | Health & social care | 2006 |
| Sirens Beauty (Ipswich) Ltd | Other services | 2010 |
| Sirius Voice & Data Ltd | Information & communication | 2010 |
| Site FIX Fenestration Ltd | Construction | 2015 |
| Site FIX Limited | Construction | 2008 |
| Site Sales Personnel Limited | Administrative & support | 2001 |
| Sivro Limited | Wholesale & retail | 2026 |
| SIX Acre Developments Ltd | Construction | 2024 |
| SIX Maple Limited | Professional & scientific | 2021 |
| Size Plumbing & Heating Limited | Construction | 2011 |
| SJ & L Public House Limited | Hospitality | 2025 |
| SJ Cordle Limited | Agriculture & fishing | 2012 |
| SJ Hairdressing & Co Ltd | Other services | 2021 |
| SJ Professional Cleaning Ltd | Administrative & support | 2025 |
| SJ Soar Roofing Ltd | Construction | 2013 |
| SJ Whinney Property Ltd | Real estate | 2021 |
| SJA Education Consultancy Limited | Professional & scientific | 2022 |
| SJA Investment Group Ltd | Real estate | 2026 |
| SJB and AVP Ltd | Wholesale & retail | 2012 |
| SJB Commercial Solutions Ltd | Professional & scientific | 2025 |
| SJC Builders Ltd | Construction | 2017 |
| SJH Contracts Limited | Construction | 2024 |
| SJH Properties Ipswich Ltd | Real estate | 2024 |
| SJH Property Consultancy Limited | Construction | 2015 |
| SJI Assets Ltd | Real estate | 2023 |
| SJK (Ipswich) Ltd | Transport & logistics | 2019 |
| SJT Sports Management Limited | Arts & recreation | 2025 |
| SK Main Limited | Real estate | 2018 |
| SK Marmaris Kebabs Ltd | Hospitality | 2023 |
| Skar Precision Mouldings Limited | Manufacturing | 1969 |
| Skel Systems Ltd | Construction | 2026 |
| Skelton Grange Farm Company Limited | Real estate | 1971 |
| Sketchbook Developments Ltd | Information & communication | 2022 |
| Skill Pro Solutions Ltd | Professional & scientific | 2024 |
| Skillinger Yachts Limited | Administrative & support | 2015 |
| Skillsarena Corporate Limited | Information & communication | 2008 |
| Skillverge Ltd | Information & communication | 2025 |
| Skin & Tonic EA Limited | Other services | 2014 |
| Skinformula Ltd | Wholesale & retail | 2025 |
| Skinner & Co Limited | Construction | 2015 |
| Skinners Fish and Chips Limited | Hospitality | 2013 |
| Skippy's Roof Racks Limited | Wholesale & retail | 2012 |
| SKK Property Management Ltd | Real estate | 2014 |
| SKM Latchmoor Investments Limited | Real estate | 2017 |
| Skorpion Limited | Transport & logistics | 2024 |
| Sky Advance Limited | Transport & logistics | 2024 |
| Sky Care Team Ltd | Administrative & support | 2024 |
| Sky High Access Limited | Administrative & support | 1987 |
| Sky Social Work Limited | Health & social care | 2025 |
| Skylark Builders Ltd | Construction | 2025 |
| Skylark Group Ltd | Financial services | 2025 |
| Skylark Haulage Ltd | Transport & logistics | 2025 |
| Skylark Living Care Ltd | Health & social care | 2026 |
| Skylarks Healthcare Ltd | Administrative & support | 2020 |
| Skyline Express Limited | Wholesale & retail | 2018 |
| Skyline S Construction Limited | Construction | 2025 |
| Skynovix Ltd | Information & communication | 2026 |
| Skyrose Services Limited | Other services | 2016 |
| Skyvio Ltd | Real estate | 2020 |
| SL Cargotrans Ltd | Transport & logistics | 2019 |
| SL Rooms Limited | Real estate | 2024 |
| SL Solutions Limited | Professional & scientific | 2018 |
| Slabiq Ltd | Transport & logistics | 2021 |
| Slaughter Limited | Other services | 2019 |
| SLC Carpentry Ltd | Manufacturing | 2021 |
| SLC Property Services Ltd | Real estate | 2026 |
| Sleeksphere Limited | Wholesale & retail | 2024 |
| Sleep NO More Ltd | Wholesale & retail | 2016 |
| Sleep Soundly Ltd | Manufacturing | 2024 |
| SLH Sports Ltd | Arts & recreation | 2023 |
| SLI Global Limited | Information & communication | 2023 |
| Slick Motion Engineering Ltd | Manufacturing | 2026 |
| SLIIII9 Holdings Ltd | Financial services | 2025 |
| Sloane Squared Ltd | Information & communication | 2011 |
| Slog & Hustle Ltd | Other services | 2016 |
| Sloper and Pearson Limited | Health & social care | 2019 |
| SM Ipswich Stores Ltd | Wholesale & retail | 2024 |
| SM Transport 2012 Limited | Transport & logistics | 2019 |
| SM Web Development Limited | Information & communication | 2025 |
| Smallboxes Accounting Ltd | Professional & scientific | 2011 |
| Smallboxes Media Ltd | Professional & scientific | 2013 |
| Smally's Biltong Ltd | Extraterritorial | 2021 |
| Smart AIM Solutions Limited | Construction | 2017 |
| Smart Bar Enterprises Ltd | Transport & logistics | 2018 |
| Smart Cart Ltd | Wholesale & retail | 2021 |
| Smart Design Blinds Ltd | Wholesale & retail | 2025 |
| Smart Guard Ltd | Construction | 2024 |
| Smart Homeseekers Limited | Real estate | 2014 |
| Smart Hub Ltd | Wholesale & retail | 2026 |
| Smart MCS Ltd | Information & communication | 2013 |
| Smart Store Ltd | Wholesale & retail | 2025 |
| Smart Student Print Limited | Professional & scientific | 2011 |
| Smart Video Tours Ltd | Information & communication | 2017 |
| Smart Warehousing Ltd | Transport & logistics | 2025 |
| Smartgraft Ltd | Administrative & support | 2025 |
| Smartkeys Property Management Ltd | Households | 2024 |
| Smartrose Health Care Limited | Administrative & support | 2024 |
| Smarts Marketing Worldwide Ltd | Information & communication | 2019 |
| Smartway Paint Ltd | Other services | 2025 |
| SMH Plastering Services Ltd | Construction | 2021 |