| Simplantex Limited | Health & social care | 2019 |
| Simplast Properties UK Limited | Real estate | 2023 |
| Simplast UK Limited | Manufacturing | 2018 |
| Simple Academic Ltd | Information & communication | 2013 |
| Simple IT Ltd | Information & communication | 2025 |
| Simple Marketing Studio Ltd | Professional & scientific | 2016 |
| Simple Online Safety Ltd | Professional & scientific | 2019 |
| Simple Online Systems Limited | Professional & scientific | 2025 |
| Simple Shine Limited | Other services | 2025 |
| Simple Taxi Hire Limited | Transport & logistics | 2025 |
| Simplicity Estates Ltd | Real estate | 2022 |
| Simplicity Property Management Ltd | Real estate | 2024 |
| Simplified Construction Solution's Ltd | Construction | 2025 |
| Simplifinance Ltd | Financial services | 2020 |
| Simply Aquatics Limited | Transport & logistics | 2009 |
| Simply Asset Consulting Ltd | Administrative & support | 2019 |
| Simply Bara Limited | Information & communication | 2025 |
| Simply Better Solutions Limited | Information & communication | 2001 |
| Simply Billericay Ltd | Health & social care | 2025 |
| Simply Capital Group Ltd | Financial services | 2017 |
| Simply Clean Ovens Limited | Administrative & support | 2012 |
| Simply CPR Limited | Health & social care | 2023 |
| Simply Crantock Limited | Hospitality | 2018 |
| Simply Frinton Ltd | Real estate | 2024 |
| Simply Honest Tech Ltd | Information & communication | 2019 |
| Simply OP 3 Ltd | Health & social care | 2019 |
| Simply OP 4 Ltd | Health & social care | 2019 |
| Simply Pure Water Limited | Hospitality | 2007 |
| Simply Siam Ltd | Other services | 2019 |
| Simply Stratford Ltd | Health & social care | 2015 |
| Simply Strings Limited | Arts & recreation | 2014 |
| Simply Transportation and Recoveries Limited | Transport & logistics | 2023 |
| Simply Uxbridge Ltd | Health & social care | 2024 |
| Simply Wimborne SPV Limited | Health & social care | 2022 |
| Simplynks Design Limited | Professional & scientific | 2019 |
| Simpson and Mclean Tooling Limited | Wholesale & retail | 2021 |
| Simpson Design Consultancy Ltd | Manufacturing | 2009 |
| Simpson Digital Ltd | Professional & scientific | 2023 |
| Simpson Engineering Consultancy Ltd | Manufacturing | 2006 |
| Simpson Lyons Estates (Kirkfield Mews) Limited | Real estate | 2014 |
| Simpson Patterns Limited | Manufacturing | 2005 |
| Simpsonian Music Limited | Arts & recreation | 2006 |
| Simsolu Limited | Wholesale & retail | 2018 |
| Simstrans Ltd | Transport & logistics | 2019 |
| Simulenta Ltd | Professional & scientific | 2026 |
| Simz(Northern) Limited | Hospitality | 2025 |
| Sin-Dtd Ltd | Wholesale & retail | 2024 |
| Sina Health Limited | Health & social care | 2014 |
| Sinclair Supply Chain Consulting Limited | Administrative & support | 2018 |
| Sinclairs Holdings Ltd | Financial services | 2024 |
| Sindale Properties Limited | Extraterritorial | 2001 |
| Sindfan Limited | Manufacturing | 2025 |
| Sindh and Co Limited | Health & social care | 2014 |
| SINDHURA2004 Limited | Health & social care | 2016 |
| SINDHURA2020 Ltd | Real estate | 2020 |
| Sinephro Records Ltd | Manufacturing | 2020 |
| Sinfoil & Slater Ltd | Wholesale & retail | 2012 |
| Sinful Ltd. | Extraterritorial | 1998 |
| Singh Financial Advisors Ltd | Other services | 2026 |
| Singh PVT Ltd | Wholesale & retail | 2020 |
| Singing in... Ltd | Education | 2020 |
| Singleton Packaging Ltd | Wholesale & retail | 2026 |
| Singspirations Ltd | Arts & recreation | 2018 |
| Singularity Forge Ltd | Construction | 2024 |
| Sinma Limited | Construction | 2017 |
| Sinmur Health Limited | Health & social care | 2026 |
| Sinoarm Limited | Wholesale & retail | 2013 |
| Sinohead Ltd | Hospitality | 2019 |
| Siobhan Hattersley Fitness Ltd | Education | 2022 |
| SIP & Savour Ltd | Wholesale & retail | 2019 |
| SIP Band Limited | Arts & recreation | 2023 |
| SIP Food Limited | Hospitality | 2024 |
| Sip'N'Dip Ltd | Hospitality | 2021 |
| Sipco Healthcare UK Ltd | Wholesale & retail | 2011 |
| Sipech Holdings Limited | Wholesale & retail | 2021 |
| Sipnspud Ltd | Hospitality | 2025 |
| Siren at Factory Limited | Arts & recreation | 2010 |
| Siren Developments Limited | Construction | 2007 |
| Siren Publishing Limited | Information & communication | 2011 |
| Siren Recordings Limited | Information & communication | 2015 |
| Sirius G Limited | Health & social care | 2013 |
| Sirius Occupational Health Limited | Health & social care | 2022 |
| Sirmacek Ltd | Hospitality | 2023 |
| SIS Beauty Limited | Other services | 2024 |
| Sisa Leisure Limited | Extraterritorial | 2019 |
| Sissons Consult Ltd | Professional & scientific | 2018 |
| Sista Bling Ltd | Wholesale & retail | 2021 |
| Sistachic Limited | Other services | 2014 |
| Sistacomps Limited | Arts & recreation | 2025 |
| Sisteme Technologies Limited | Information & communication | 2023 |
| Sister Haus Ltd | Other services | 2025 |
| Sister Properties Limited | Education | 2013 |
| Sister Sister Haulage Ltd | Administrative & support | 2017 |
| Site Support Hub Ltd | Information & communication | 2026 |
| Sitecoms Limited | Extraterritorial | 2011 |
| Sitehaul Ltd | Water & waste | 2022 |
| Siti Personnel Ltd | Professional & scientific | 2025 |
| Sitwell Estates NO 1 Company Limited | Extraterritorial | 2023 |
| Sitwell Estates NO 2 Company Limited | Extraterritorial | 2023 |
| Sitwell Estates NO 3 Company Limited | Extraterritorial | 2023 |