| Silent Partners Limited | Arts & recreation | 1992 |
| Silentheart Ltd | Wholesale & retail | 2019 |
| Silenus Fire Protection Ltd | Construction | 2025 |
| Silenus Property Ltd. | Construction | 2007 |
| Silkstrandzs Ltd | Wholesale & retail | 2025 |
| Silkypet Ltd | Wholesale & retail | 2026 |
| Silvecko Ltd | Information & communication | 2025 |
| Silven Traders Ltd | Wholesale & retail | 2025 |
| Silver Knight Air Conditioning Limited | Energy | 2008 |
| Silver Knight Holdings Ltd | Real estate | 2017 |
| Silver Oaks Lettings Ltd | Real estate | 2026 |
| Silverend Car Sales Limited | Wholesale & retail | 2010 |
| Silverlake Education Limited | Education | 2023 |
| Silverloom Enterprises Ltd | Wholesale & retail | 2026 |
| Silverwood (Wombourne) Management Limited | Households | 2008 |
| Simark Construction Limited | Construction | 2001 |
| Simba Nature Ltd | Wholesale & retail | 2022 |
| Simclick Floors Trade Centre Limited | Wholesale & retail | 2014 |
| Sime's Transport Limited | Transport & logistics | 2022 |
| Simi Property Ltd | Real estate | 2026 |
| Simkim Foods Ltd | Wholesale & retail | 2019 |
| Simlex Group Limited | Manufacturing | 1945 |
| Simmfoods Ltd | Hospitality | 2025 |
| Simmill Investments Limited | Real estate | 2012 |
| Simms Projects Limited | Professional & scientific | 2023 |
| Simon Beviss Ltd | Construction | 2008 |
| Simon Developments Limited | Administrative & support | 1988 |
| Simon Homes Limited | Administrative & support | 1981 |
| Simona Transport Ltd | Transport & logistics | 2018 |
| Simonds Consultancy Limited | Professional & scientific | 2001 |
| Simplay Rugs Limited | Wholesale & retail | 2011 |
| Simple Bookkeeping (UK) Ltd | Professional & scientific | 2021 |
| Simple Business Systems Limited | Information & communication | 2012 |
| Simple Creative Marketing Limited | Professional & scientific | 2012 |
| Simplewarm Ltd | Wholesale & retail | 2016 |
| Simplista Ltd | Information & communication | 2009 |
| Simply Breathtaking Ltd | Other services | 2021 |
| Simply Coffee Shops Limited | Construction | 2010 |
| Simply DAL Ltd | Other services | 2020 |
| Simply Drinks World Limited | Wholesale & retail | 2018 |
| Simply DRY Limited | Wholesale & retail | 2012 |
| Simply Interiors (Midlands) Ltd | Construction | 2012 |
| Simply Mocktails Ltd | Hospitality | 2022 |
| Simply Properties Limited | Real estate | 2002 |
| Simply Retail Nationwide Ltd | Real estate | 2025 |
| Simply Supermarket Limited | Wholesale & retail | 2025 |
| Simplypostered Ltd | Wholesale & retail | 2026 |
| Simran Arora Takeaway Ltd | Hospitality | 2020 |
| Simran Beauty Salon Ltd | Other services | 2024 |
| Simran Development Ltd | Real estate | 2024 |
| Simran's Social Care Services Ltd | Health & social care | 2022 |
| Simrit Bains Ltd | Information & communication | 2024 |
| Sinai Care Solutions Limited | Hospitality | 2016 |
| Since Sixty Eight Interiors Ltd | Professional & scientific | 2024 |
| Sincerity Funerals & Flowers Ltd | Other services | 2025 |
| Sincerity Funerals Ltd | Other services | 2017 |
| Sinclair Land and Leisure Limited | Real estate | 1979 |
| Sinclere Electrical Installation & Panel Wiring Ltd | Construction | 2025 |
| Sindybats Limited | Health & social care | 2021 |
| Sinead Environmental Ltd | Information & communication | 2019 |
| Singapuriye Nail & Beauty Salon Ltd | Other services | 2025 |
| Singh Auto Care Ltd | Wholesale & retail | 2025 |
| Singh Brother Services Ltd | Wholesale & retail | 2020 |
| Singh Brothers Holdings Ltd | Financial services | 2026 |
| Singh Brothers Sutton Ltd | Wholesale & retail | 2026 |
| Singh Builders MCR Ltd | Construction | 2019 |
| Singh Building and Landscaping Ltd | Extraterritorial | 2024 |
| Singh Carriers Ltd | Transport & logistics | 2026 |
| Singh Prime Property Ltd | Real estate | 2025 |
| Singh Recovery Ltd | Transport & logistics | 2024 |
| Singh Sprinter Spares Ltd | Wholesale & retail | 2025 |
| Singh Workx Ltd | Professional & scientific | 2026 |
| Singhsbury Local OFF License Ltd | Wholesale & retail | 2019 |
| Singhz Construction Limited | Construction | 2023 |
| Sinka Ltd | Health & social care | 2019 |
| Siolma Limited | Construction | 2024 |
| Sira Housing Ltd | Real estate | 2024 |
| Sirdaar Company Limited | Hospitality | 2010 |
| Sirji Limited | Wholesale & retail | 2018 |
| Sisb Properties Ltd | Real estate | 2024 |
| Sisko Trading Limited | Construction | 2024 |
| SISTER2SISTER C.I.C. | Education | 2020 |
| Sisterhood Health Care Limited | Health & social care | 2021 |
| Sisyphusdesigns Ltd | Construction | 2025 |
| Sisyphusfx Ltd | Professional & scientific | 2025 |
| Site Bright Limited | Wholesale & retail | 2016 |
| Site Plant Centre Limited | Administrative & support | 2021 |
| Site-Shield Limited | Construction | 2023 |
| Sitecore Services Limited | Construction | 2026 |
| Sitelink Computer Consultants Limited | Information & communication | 1996 |
| Sithundu Ltd | Manufacturing | 2022 |
| Siuta Ltd | Wholesale & retail | 2026 |
| SIX String Supplies Ltd | Wholesale & retail | 2014 |
| SIX Three Marketing and Media Limited | Information & communication | 2024 |
| Sixth DAN Investments Limited | Wholesale & retail | 1985 |
| Sixth Fold Ministry Ltd | Information & communication | 2025 |
| Sizzlers Kebab and Pizza Limited | Hospitality | 2026 |
| SJ Baker Social Limited | Hospitality | 2024 |
| SJ Dixon Carver Limited | Wholesale & retail | 2014 |
| SJ Elite Properties Limited | Real estate | 2025 |