| Silverhouse Management Limited | Professional & scientific | 2022 |
| Silvermd Ltd | Transport & logistics | 2019 |
| Silverstone Corporation Limited | Administrative & support | 2012 |
| Silverstone Factors Limited | Other services | 1986 |
| Silverstone Riding School Limited | Arts & recreation | 2014 |
| Silverstone Security Limited | Administrative & support | 2017 |
| Silverwood Equities Ltd | Financial services | 2023 |
| Silviad Construction Ltd | Construction | 2025 |
| Silviu and Chris Limited | Transport & logistics | 2015 |
| SIM Build Solutions Ltd | Manufacturing | 2024 |
| SIM Cleaning Solutions Ltd | Administrative & support | 2026 |
| Sima Perfect Care Limited | Health & social care | 2017 |
| Simat Aerials Limited | Construction | 2003 |
| Simba & Partners Limited | Professional & scientific | 2019 |
| Simba Logistics Ltd | Transport & logistics | 2024 |
| Simba Transport Limited | Transport & logistics | 2014 |
| Simbest Accounting Services Limited | Professional & scientific | 2018 |
| Simeon James Nutrition Fitness Ltd | Other services | 2021 |
| Simitate Ltd | Manufacturing | 2024 |
| Simmons Family Holdings Limited | Financial services | 2022 |
| Simmovate Ltd | Professional & scientific | 2025 |
| Simms Consulting Limited | Professional & scientific | 2017 |
| Simo Groupwork Ltd | Construction | 2025 |
| Simon Barker Roofing Limited | Construction | 2007 |
| Simon Boots Psychotherapy Services Limited | Health & social care | 2010 |
| Simon Dolman Limited | Real estate | 2025 |
| Simon Howard Property Investments Ltd | Real estate | 2018 |
| Simon Installations Limited | Manufacturing | 2026 |
| Simon Jones GPM Ltd | Construction | 2021 |
| Simon Sweetland Ltd | Construction | 2005 |
| Simon Vlad Construction Ltd | Construction | 2019 |
| Simon@Didie Ltd | Health & social care | 2014 |
| Simoni Crystal Cleaning Ltd | Administrative & support | 2026 |
| Simon’S Outdoor Spaces Ltd | Administrative & support | 2024 |
| Simple Diverse Solutions Limited | Extraterritorial | 2021 |
| Simple Jewels Ltd | Wholesale & retail | 2018 |
| Simple Pension Advice Limited | Professional & scientific | 2025 |
| Simple Sessions Ltd | Arts & recreation | 2017 |
| SIMPLI2FORM Limited | Professional & scientific | 2024 |
| Simplicity Enterprises Ltd | Wholesale & retail | 2020 |
| Simply Afro Foods Ltd | Wholesale & retail | 2024 |
| Simply Beautiful Concepts Ltd | Wholesale & retail | 2016 |
| Simply BIN Cleaning Ltd | Other services | 2022 |
| Simply Bookkeeping & Accounting Ltd | Professional & scientific | 2026 |
| Simply Business Services Limited | Financial services | 2025 |
| Simply Card Payments Ltd | Information & communication | 2026 |
| Simply Commspace Limited | Construction | 2025 |
| Simply Convenience Store Ltd | Wholesale & retail | 2015 |
| Simply Elegant Events Ltd | Administrative & support | 2025 |
| Simply Innovate Limited | Information & communication | 2003 |
| Simply IT (Northampton) Limited | Information & communication | 2011 |
| Simply Management Limited | Professional & scientific | 2019 |
| Simply Mart Ltd | Wholesale & retail | 2022 |
| Simply Reliable Parts UK Ltd | Wholesale & retail | 2026 |
| Simply Resolved Ltd | Other services | 2024 |
| Simply Scented Ltd | Wholesale & retail | 2021 |
| Simply Sicily Ltd | Hospitality | 2020 |
| Simply Techspace Limited | Other services | 2021 |
| Simply Workshops Limited | Professional & scientific | 2021 |
| Simply Workspace Ltd | Other services | 2018 |
| Simply Yumyum Ltd | Hospitality | 2024 |
| Simplytalkingtherapy Limited | Health & social care | 2019 |
| Simpson Catering Investments Limited | Real estate | 2016 |
| Simpson Catering Pubs Limited | Hospitality | 2016 |
| Sims Enterprise Ltd | Information & communication | 2021 |
| Sims Healthcare Ltd | Health & social care | 2014 |
| Simsek Consulting Ltd | Information & communication | 2021 |
| Simstaff Ltd | Information & communication | 2021 |
| Simul Holdings Limited | Financial services | 2018 |
| Simvaly Ltd | Construction | 2015 |
| SIN Cars UK Limited | Wholesale & retail | 2013 |
| Sinai Consultancy Ltd. | Financial services | 2016 |
| Sinanzeni Chimutengo Limited | Health & social care | 2015 |
| Sinar Anglo Polish Enterprises Limited | Extraterritorial | 1982 |
| Sinc Energy Ltd | Information & communication | 2026 |
| Sinclair High Ticket Sales Limited | Administrative & support | 2025 |
| Sinclair HR Solutions Limited | Administrative & support | 2013 |
| Sindy Ndlovu Healthcare Limited | Health & social care | 2024 |
| Sine-Wave Studios Ltd | Other services | 2025 |
| Sing Long Limited | Wholesale & retail | 2014 |
| Sing Openly Limited | Arts & recreation | 2025 |
| Single Marque Events Limited | Arts & recreation | 2008 |
| Single Thread Consulting Limited | Professional & scientific | 2024 |
| Singular Cycles Limited | Wholesale & retail | 2006 |
| Singular Yachting Group Ltd | Wholesale & retail | 2024 |
| Sino-British Trade Alliance Limited | Administrative & support | 2018 |
| Sinter Site Services Limited | Extraterritorial | 2016 |
| Sinu Trans Ltd | Transport & logistics | 2018 |
| SIO International Ltd | Professional & scientific | 2020 |
| Siokri Asset Management Ltd | Extraterritorial | 2020 |
| Siokri Leisure (UK) Ltd | Extraterritorial | 2024 |
| Sion Health Care Services Limited | Education | 2015 |
| SIP + Shuck Limited | Hospitality | 2026 |
| SIP and Olive Ltd | Hospitality | 2025 |
| Sipearl UK Limited | Manufacturing | 2024 |
| Sipexa Ltd | Wholesale & retail | 2016 |
| Sipra Store UK Ltd | Wholesale & retail | 2026 |
| Sips.Uk Ltd | Manufacturing | 2004 |
| Sirbu Installation Ltd | Construction | 2023 |
| Sirbu Properties Ltd | Real estate | 2025 |