| Simplyrfmw Limited | Information & communication | 2024 |
| Sims Building Limited | Construction | 2015 |
| Sims Joinery Limited | Construction | 2015 |
| Sims Telecoms Ltd | Information & communication | 2021 |
| Sims Welding & Fabrication Limited | Manufacturing | 2017 |
| Singergise Limited | Other services | 2016 |
| Singhz Properties Management Ltd | Real estate | 2017 |
| Sinnybaby Estates Limited | Real estate | 2021 |
| Sinnybaby Media Ltd | Information & communication | 2020 |
| Sinnybaby Promotions Ltd | Arts & recreation | 2020 |
| Siren Adventures Ltd | Professional & scientific | 2024 |
| Siren Systems Limited | | 1988 |
| Sirhowy Logistics Ltd | Transport & logistics | 2019 |
| Sirhowy Valley Hub C.I.C. | Hospitality | 2022 |
| Siri Phones Ltd | Wholesale & retail | 2025 |
| Sirius Dining IOW Ltd | Hospitality | 2023 |
| Siskin Labs Ltd | Professional & scientific | 2020 |
| Sisters in Sync Ltd | Wholesale & retail | 2023 |
| Site Appraisals Limited | Professional & scientific | 2005 |
| Site Facilities Solutions Limited | Construction | 2014 |
| Sittingbourne Rugby Union Football Club Limited | Arts & recreation | 2017 |
| Situations Vacant Ltd | Administrative & support | 2016 |
| SIX Forward Ltd | Professional & scientific | 2009 |
| SIX Towns PUB Company Ltd | Hospitality | 2018 |
| Sixyards Ltd | Real estate | 2021 |
| SJ Banks Hygienist Ltd | Health & social care | 2024 |
| SJ Capital Holdings Ltd | Real estate | 2025 |
| SJ Caring Ltd | Health & social care | 2020 |
| SJ Gymfit Ltd | Wholesale & retail | 2025 |
| SJ Learning & Development Consultancy Ltd | Professional & scientific | 2023 |
| SJ Legal Risk Ltd | Professional & scientific | 2020 |
| SJ Property Ventures Ltd | Real estate | 2024 |
| SJ Williams Property Limited | Real estate | 2020 |
| SJ Workforce Limited | Construction | 2018 |
| SJA Aero Ltd | Administrative & support | 2021 |
| SJB Drywall (Shropshire) Ltd | Construction | 2023 |
| SJC Logistics Ltd | Financial services | 2026 |
| Sjconsumers Ltd | Wholesale & retail | 2025 |
| SJD Management Solutions Ltd | Professional & scientific | 2022 |
| SJD Stacs Ltd | Wholesale & retail | 2014 |
| SJH Fishing Ltd | Agriculture & fishing | 2023 |
| SJM Accommodation Ltd | Real estate | 2020 |
| SJM Architectural Services Ltd | Professional & scientific | 2016 |
| SJP Design Ltd | Wholesale & retail | 2024 |
| SJR Invest Limited | Information & communication | 2022 |
| SJS Asbestos Ltd | Transport & logistics | 2023 |
| SJS Properties (Wales) Limited | Real estate | 1974 |
| SJT Electrical Supplies Limited | Wholesale & retail | 1982 |
| SK & AZ Enterprises Ltd | Transport & logistics | 2026 |
| SK Lloyd Ltd | Professional & scientific | 2025 |
| Skan Group Ltd | Transport & logistics | 2025 |
| Skenfrith Mews Management Company Limited | Extraterritorial | 2003 |
| Skerryvore Space Limited | Real estate | 2023 |
| Skillsafe Mentoring Ltd | Education | 2023 |
| Skin Sleeps Ltd | Manufacturing | 2026 |
| Skinny Nannies Ltd | Wholesale & retail | 2024 |
| Skinsmyth Limited | Health & social care | 2020 |
| SKM Scaffolding Ltd | Construction | 2026 |
| SKN Property Limited | Real estate | 2017 |
| Sky LUX Nail Ltd | Other services | 2026 |
| Sky Textile Ltd | Wholesale & retail | 2024 |
| Sky's the Limit Homes Ltd | Real estate | 2021 |
| Skydazzle Ltd | Arts & recreation | 2010 |
| Skyfamilytrip Ltd | Real estate | 2025 |
| Skyla & Finley Holdings Limited | Financial services | 2025 |
| Skyline Carpentry & Building Ltd | Manufacturing | 2017 |
| Skyline Contractors Group Ltd | Construction | 2019 |
| Skylite-Wales Limited | Administrative & support | 2017 |
| Skyno Ltd | Wholesale & retail | 2026 |
| Skyscrapers Building Services Ltd. | Construction | 2018 |
| Skyward Animation Limited | Information & communication | 2023 |
| Skyward Films Limited | Information & communication | 2023 |
| SL & AP Limited | Professional & scientific | 2013 |
| SL Buying Service Ltd | Wholesale & retail | 2022 |
| Slainte Highland Spirits Limited | Manufacturing | 2016 |
| Slate Consult Limited | Professional & scientific | 2018 |
| Slate Legal Limited | Professional & scientific | 2015 |
| Slayer Limited | Administrative & support | 2021 |
| SLC Property Management Limited | Real estate | 2014 |
| Sleightholme Sports Promotions Ltd | Arts & recreation | 2024 |
| SLF Ventilation Services Ltd | Administrative & support | 2019 |
| Slga Consultancy Ltd | Professional & scientific | 2023 |
| Slipping Jimmy's Limited | Hospitality | 2015 |
| SLJ Associates Limited | Professional & scientific | 2022 |
| Slocombe Property Services Limited | Wholesale & retail | 2003 |
| Slopers Ltd | Hospitality | 2023 |
| Slotte Ltd | Professional & scientific | 2018 |
| SM Carpentry IOW Ltd | Construction | 2023 |
| SM Newport Foods Ltd | Hospitality | 2026 |
| Small Acres Estates Limited | Real estate | 2025 |
| Smaller Developments Limited | Construction | 2015 |
| Smart Fones 4 U Ltd | Manufacturing | 2019 |
| Smart Home Serve Ltd | Construction | 2024 |
| Smart Products Collection Ltd | Wholesale & retail | 2026 |
| Smart Roofing Cardiff Limited | Construction | 2016 |
| Smart Shack Limited | Education | 2020 |
| Smart Training and Recruitment Limited | Education | 2003 |
| Smart Vision for Information Systems UK Ltd | Extraterritorial | 2017 |
| Smarter Farms Ltd | Professional & scientific | 2019 |
| Smarter Glazing Solutions Ltd | Construction | 2024 |