| Silverstone Developers Limited | Real estate | 2025 |
| Silverstone Enterprises & Services Ltd | Real estate | 2026 |
| Silverstones Holdings Limited | Wholesale & retail | 2025 |
| Silversync Limited | Wholesale & retail | 2024 |
| Silvertown Services Ltd | Administrative & support | 2023 |
| Silverwel Limited | Wholesale & retail | 2025 |
| SIM Brickworks Ltd | Construction | 2019 |
| SIM Civil Construction Ltd | Construction | 2014 |
| SIM Serv Ltd | Construction | 2016 |
| Simanay Limited | Real estate | 2025 |
| Simao UK. Ltd | Wholesale & retail | 2025 |
| Simar Investments Limited | Real estate | 2024 |
| Simar Limited | Wholesale & retail | 2012 |
| Simba Contracts Ltd | Construction | 2007 |
| Simbarock Ltd | Wholesale & retail | 2023 |
| Simbas Shop Ltd | Arts & recreation | 2021 |
| Simchi Network Ltd | Information & communication | 2026 |
| Simms Investments Limited | Real estate | 2017 |
| Simo Property Group Ltd | Real estate | 2022 |
| Simon & Sandra Ltd | Real estate | 2020 |
| Simpatico Partners Limited | Financial services | 2017 |
| Simplatech Ltd | Wholesale & retail | 2023 |
| Simple Auto Solutions Ltd | Professional & scientific | 2026 |
| Simple CAB Dispatch Ltd | Information & communication | 2018 |
| Simple Cell Solutions Ltd | Wholesale & retail | 2023 |
| Simple Electrical Solutions Ltd | Construction | 2025 |
| Simple Engineering Energy Solutions Ltd | Professional & scientific | 2026 |
| Simple Lettings Ltd | Real estate | 2018 |
| Simple Meds Limited | Public administration | 2022 |
| Simple Savings London Limited | Wholesale & retail | 2026 |
| Simple Services London Ltd | Administrative & support | 2020 |
| Simple Slides Limited | Manufacturing | 2011 |
| Simple Touch Limited | Administrative & support | 2026 |
| Simplified Properties Services Ltd | Real estate | 2018 |
| Simply Accounting LDN Ltd | Professional & scientific | 2025 |
| Simply Anaa LLP | | 2022 |
| Simply Build and Renovation Ltd | Construction | 2026 |
| Simply Create Ltd | Information & communication | 2018 |
| Simply Green Glazing Solutions Ltd | Manufacturing | 2020 |
| Simply Heating & Plumbing Ltd | Construction | 2025 |
| Simply Mechanics Ltd | Wholesale & retail | 2024 |
| Simply Pizza Ltd | Hospitality | 2024 |
| Simply Reach Limited | Wholesale & retail | 2020 |
| Simply Shirley's Ltd | Manufacturing | 2019 |
| Simply Smart Solutions Ltd | Information & communication | 2021 |
| Simply Vibe Limited | Wholesale & retail | 2012 |
| Simran Raisha Limited | Wholesale & retail | 2026 |
| Simran Realty Group Ltd | Real estate | 2025 |
| Simran Shop Ltd | Wholesale & retail | 2025 |
| Simranjeet SINGH1 Ltd | Construction | 2025 |
| Sims Hair and Beauty Global Ltd | Construction | 2023 |
| Sims Hair and Beauty GPB Ltd | Construction | 2021 |
| Simsoft Technology Limited | Information & communication | 2024 |
| Sinas Consulting Ltd | Professional & scientific | 2022 |
| Sinaz Services Ltd | Administrative & support | 2017 |
| Sinclair Dalapa Limited | Wholesale & retail | 1995 |
| Sinclair Engineering Limited | Wholesale & retail | 2019 |
| Sinclair Financial Ltd | Financial services | 2014 |
| Sindhi Association of Europe Ltd | Administrative & support | 2025 |
| Sindhu Immigration Services Ltd. | Professional & scientific | 2015 |
| Sindhu Properties and Developers Ltd | Real estate | 2023 |
| Singam Bay Ltd | Hospitality | 2022 |
| Singer & James Limited | Real estate | 1976 |
| Singer House Ltd | Real estate | 2025 |
| Singh & Gupta Ltd | Construction | 2022 |
| Singh Building Supplies Ltd | Wholesale & retail | 2021 |
| Singh Carpentry & Joinery Ltd | Construction | 2010 |
| Singh Carpentry Ltd | Construction | 2026 |
| Singh Design & Construction Ltd | Construction | 2026 |
| Singh Food Tiffin Services & Catering Limited | Hospitality | 2022 |
| Singh Landscape Expert Ltd | Administrative & support | 2020 |
| Singh Saheb Limited | Construction | 2023 |
| Singh Security Services Ltd | Administrative & support | 2025 |
| Singh UK Courier Ltd | Transport & logistics | 2022 |
| Singhs Legal Assist Ltd | Professional & scientific | 2024 |
| Singhsberry Fruit and Vegetable Limited | Wholesale & retail | 2021 |
| Singhsberry Ilford Ltd | Wholesale & retail | 2026 |
| Sinha Ltd | Real estate | 2023 |
| Sinma Electrics Ltd | Administrative & support | 2016 |
| Sino Sova Limited | Other services | 2018 |
| Sinon Property Ltd | Real estate | 2024 |
| Sinope Limited | Hospitality | 2026 |
| Sinshey PAY Ltd | Real estate | 2008 |
| SINTRANSPORT89 Ltd | Transport & logistics | 2020 |
| SIO Electrical Services Ltd | Construction | 2019 |
| SIP Group Limited | Professional & scientific | 2004 |
| Sipca Limited | Real estate | 2021 |
| Sipca Property Limited | Real estate | 2023 |
| Sipster Limited | Wholesale & retail | 2025 |
| SIR Aulakh Group Ltd | Construction | 2024 |
| SIR Robert Construction Ltd | Construction | 2023 |
| SIR Wood Ltd | Construction | 2019 |
| Sira Production Studios Limited | Manufacturing | 2023 |
| Siraj Property Limited | Real estate | 2025 |
| Sirat Holdings Ltd | Real estate | 2024 |
| Sirbu Construction Ltd | Construction | 2023 |
| Sireio Ltd | Information & communication | 2026 |
| Sirg Enterprise Ltd | Wholesale & retail | 2026 |
| Siri Health Care Solutions Ltd | Health & social care | 2022 |
| Siris Trading Ltd | Wholesale & retail | 2017 |