| Sinava Limited | Wholesale & retail | 2018 |
| Sincere Homecare Ltd | Health & social care | 2022 |
| Sinceresponse C.I.C. | Education | 2019 |
| Sinclair Assets Limited | Financial services | 2023 |
| Sinclair Building Developments Limited | Construction | 2020 |
| Sinclair Contracting Services Ltd | Information & communication | 2014 |
| Sinclair Smart Coding Limited | Manufacturing | 2024 |
| Sindal Construction Ltd | Construction | 2017 |
| Sindhi Systems Ltd | Wholesale & retail | 2005 |
| Singh & Kaur Properties Ltd | Households | 2018 |
| Singh (UK) Limited | Wholesale & retail | 2013 |
| Singh and Daughters Property Developments Ltd | Real estate | 2024 |
| Singh Brothers Haulage Ltd | Transport & logistics | 2025 |
| Singh Builders Midlands Ltd | Construction | 2024 |
| Singh Constructions and Properties Ltd | Construction | 2024 |
| Singh Custom Prints Ltd | Manufacturing | 2026 |
| Singh Electrical Services Ltd | Construction | 2025 |
| Singh Holdings Ltd | Real estate | 2020 |
| Singh Midlands Ltd | Transport & logistics | 2026 |
| Singh Pourgourides Associates Ltd | Health & social care | 2020 |
| Singh Properties (Leicester) Ltd | Real estate | 2017 |
| Singh Property Rental Ltd | Real estate | 2026 |
| Singh Readymix Concrete Ltd | Construction | 2020 |
| Singh Saab Limited | Transport & logistics | 2019 |
| Singh Sales and Marketing Ltd | Wholesale & retail | 2023 |
| Singh Solid Build Ltd | Construction | 2025 |
| Singh Trucking Ltd | Transport & logistics | 2007 |
| Singhbit Ltd | Other services | 2021 |
| Singhs Phone Solutions Ltd | Wholesale & retail | 2020 |
| Sinnab Limited | Health & social care | 2023 |
| Sinouk Prochain Sourcing Limited | Wholesale & retail | 2026 |
| Sinroja Homes Limited | Real estate | 2020 |
| Sinroja Investments Ltd | Financial services | 2024 |
| Sinroja Motorcycles Limited | Wholesale & retail | 2020 |
| Sintek Limited | Other services | 1985 |
| SIP Play Cafe Ltd | Hospitality | 2025 |
| Siphon Limited | Information & communication | 1998 |
| SIR & Dippity Productions Ltd | Information & communication | 2025 |
| SIR Umer Cutting UK Ltd | Manufacturing | 2017 |
| Sire Holdings 2 Limited | Real estate | 2024 |
| Sirh Consulting Limited | Information & communication | 2016 |
| Siris Capital Limited | Real estate | 2016 |
| Sirius (Korea) Limited | Financial services | 1999 |
| Sirrs Motor Company Ltd | Wholesale & retail | 2013 |
| Sisa Information Security Ltd | Information & communication | 2016 |
| Siserve Limited | Manufacturing | 2003 |
| Sisodia Associates Ltd | Administrative & support | 2026 |
| Sisodia Estates Ltd | Real estate | 2017 |
| Sisodia Property Services Ltd | Financial services | 2023 |
| Sisonke Limited | Administrative & support | 2010 |
| Sistem Carpentry Limited | Construction | 2006 |
| Sisters & Studio Ltd | Arts & recreation | 2026 |
| Sisters Hood Ltd | Hospitality | 2025 |
| Sisters Investments Ltd | Financial services | 2018 |
| Sisu Property Limited | Real estate | 2021 |
| Sita Property Group Ltd | Real estate | 2025 |
| Site Access Services Ltd | Construction | 2019 |
| Site Wide UK Limited | Information & communication | 2016 |
| Sitemaster Services Ltd | Financial services | 2022 |
| Sitepath Limited | Manufacturing | 2009 |
| Sitewire Limited | Real estate | 2023 |
| Sitka AD Ltd | Transport & logistics | 2023 |
| Sitrys Ltd | Information & communication | 2014 |
| Siva Services Limited | Real estate | 2018 |
| Sivaharan Holdings Limited | Financial services | 2026 |
| Sivan Estates Limited | Real estate | 2021 |
| Sivasothy Limited | Real estate | 2023 |
| Siviansh Ltd | Wholesale & retail | 2024 |
| Siwak Haus Ltd | Manufacturing | 2025 |
| SIX Ellis Limited | Real estate | 2016 |
| SIX Feet Ltd | Information & communication | 2022 |
| SIX Hill Bar Ltd | Hospitality | 2018 |
| SIX to TEN Limited | Wholesale & retail | 2014 |
| Sixties Consultancy Limited | Professional & scientific | 2023 |
| Sixtwoeight Design Ltd | Information & communication | 2023 |
| Siya Jeram Consultancy Ltd | Professional & scientific | 2019 |
| Siya Medical Ltd | Health & social care | 2016 |
| Siya's Kitchen Ltd | Manufacturing | 2026 |
| Sizie's Care Limited | Health & social care | 2017 |
| Sizzlers Banqueting Ltd | Hospitality | 2020 |
| SJ 83 Limited | Financial services | 2013 |
| SJ and JT Properties LLP | | 2023 |
| SJ Approved Used Cars Ltd | Wholesale & retail | 2020 |
| SJ Auto Traders Limited | Wholesale & retail | 2025 |
| SJ Building Services Ltd | Construction | 2024 |
| SJ Cheema PTY Ltd | Wholesale & retail | 2023 |
| SJ Design Technology Ltd | Information & communication | 2023 |
| SJ Mach Property Limited | Real estate | 2023 |
| SJ Residency Limited | Hospitality | 2020 |
| SJ Walters Electrical Limited | Construction | 2022 |
| SJ Whittle Ltd | Professional & scientific | 2026 |
| Sj's Cafe Ltd | Hospitality | 2022 |
| Sj's Dining Ltd | Hospitality | 2025 |
| SJ10 Ltd | Manufacturing | 2018 |
| SJ5 Transport Ltd | Transport & logistics | 2026 |
| SJA Enterprise Ltd | Professional & scientific | 2023 |
| SJA Site Services Ltd | Construction | 2015 |
| SJA Taylor Plumbing & Heating Ltd | Construction | 2015 |
| SJB Products Ltd | Wholesale & retail | 2020 |
| SJB Wealth Ltd | Financial services | 2026 |