| Sinclairhill Chargeholder Limited | Real estate | 2021 |
| Sind Consulting Ltd | Education | 2022 |
| Sines Parks (S.E.) Limited | Administrative & support | 2007 |
| Sines Parks Holdings Limited | Financial services | 2012 |
| Sines Parks Ltd | Hospitality | 2003 |
| Sines Parks Luxury Living Limited | Hospitality | 2017 |
| Sines Parks Luxury Services Limited | Hospitality | 2019 |
| Sines Parks Residential Limited | Real estate | 2008 |
| Sinevis Technologies UK Ltd | Wholesale & retail | 2021 |
| Singcore London Limited | Real estate | 2024 |
| Singh & Co (Vegfruit) Limited | Wholesale & retail | 1977 |
| Singh Healthcare (UK) LLP | | 2011 |
| Singh Healthcare Investments Limited | Real estate | 2011 |
| SINGH22 Ltd | Real estate | 2026 |
| Singhai Medical Limited | Health & social care | 2019 |
| Singsongbird School of Singing Ltd | Education | 2026 |
| Sinister Limited | Manufacturing | 2025 |
| Sinnu 1 Ltd | Wholesale & retail | 2023 |
| Sino Reit Ltd | Real estate | 2016 |
| Sinosweet (UK) Limited | Professional & scientific | 2014 |
| Sinton Andrews Surveyors LLP | | 2010 |
| Sioaas Limited | Health & social care | 2024 |
| Siobahn & Co Limited | Wholesale & retail | 2017 |
| Siomma Smiles Limited | Health & social care | 2017 |
| SIP N Spice Ltd | Wholesale & retail | 2025 |
| Sipnslice Ltd | Wholesale & retail | 2025 |
| Sipson Cars Limited | Wholesale & retail | 2020 |
| SIR Alexander Road Management Limited | Households | 1992 |
| SIR Reel Limited | Information & communication | 2019 |
| Sircj Limited | Administrative & support | 2013 |
| Sire Consulting Ltd | Administrative & support | 2019 |
| Siri Infosolutions PVT Ltd | Information & communication | 2026 |
| Sirimon Consulting Ltd | Professional & scientific | 2019 |
| Sirius IT Solutions Limited | Information & communication | 2011 |
| Siso Solutions Limited | Information & communication | 2008 |
| Sison Realty LLP | | 2024 |
| Sita Optical Ltd | Wholesale & retail | 2022 |
| Sitara Lounge Limited | Hospitality | 2025 |
| Sitaram Events Limited | Hospitality | 2025 |
| Site Safe International Ltd | Financial services | 2021 |
| Sitesage Limited | Real estate | 2025 |
| Sits London Limited | Wholesale & retail | 2018 |
| Situ Cornerstone Ltd | Transport & logistics | 2021 |
| Situzen Limited | Professional & scientific | 2017 |
| Siuntu Bite Limited | Transport & logistics | 2020 |
| Siva Technical Solutions Ltd | Education | 2026 |
| Sivaaji Optical X Ltd | Health & social care | 2019 |
| Sivaguru Properties Ltd | Real estate | 2018 |
| Sivak Accountancy Limited | Professional & scientific | 2005 |
| Sivanesa Engineering Ltd | Construction | 2018 |
| Sivasakthi Kshetraa-Dance School Limited | Education | 2023 |
| Sivasoruban Medical Limited | Health & social care | 2019 |
| Sivenson Ltd | Professional & scientific | 2020 |
| Sivika Associates Ltd | Construction | 2013 |
| SIX Bells Investments Limited | Hospitality | 2013 |
| SIX Face Innovations Ltd | Financial services | 2018 |
| SIX Star AG Limited | Real estate | 2020 |
| SIX Star Tech Limited | Administrative & support | 2006 |
| Sixberries Ltd | Information & communication | 2013 |
| Sixems Properties Ltd | Real estate | 2025 |
| Sixth LAB Limited | Manufacturing | 2025 |
| Sixty Park Street Limited | Real estate | 2022 |
| Siya Designs Ltd | Professional & scientific | 2024 |
| Siya International Limited | Information & communication | 2016 |
| Siyal Baraka Ltd | Hospitality | 2018 |
| Siyam World Limited | Wholesale & retail | 2020 |
| Siyana Hemani Ltd | Other services | 2017 |
| Siyani Holdings Ltd | Information & communication | 2024 |
| Siyani Investments Ltd | Households | 2012 |
| Siyatex Ltd | Wholesale & retail | 2019 |
| Siyt Homes Ltd | Real estate | 2026 |
| Sizzlin Sisters Ltd | Hospitality | 2025 |
| SJ Advance Painters Limited | Construction | 2024 |
| SJ Consultancy Harrow Ltd | Professional & scientific | 2023 |
| SJ Home Care Limited | Health & social care | 2021 |
| SJ Pharmacare Limited | Health & social care | 2018 |
| SJC Imports Limited | Wholesale & retail | 2021 |
| SJE Universal Limited | Hospitality | 2012 |
| Sjgloble Limited | Wholesale & retail | 2025 |
| SJJ Estates Limited | Households | 2017 |
| Sjmv Property Ltd | Real estate | 2022 |
| SJO Care Limited | Professional & scientific | 2024 |
| SJP Food and Wine Limited | Wholesale & retail | 2024 |
| SJP Property Investments Limited | Professional & scientific | 2018 |
| Sjpc Project Management Limited | Construction | 2019 |
| Sjpt Properties Limited | Real estate | 2017 |
| SJR Investing Limited | Real estate | 2019 |
| Sjrm Ltd | Health & social care | 2018 |
| Sjsb Ltd | Wholesale & retail | 2025 |
| SJT Coach Limited | Transport & logistics | 2019 |
| SJZ Medical Services Limited | Health & social care | 2017 |
| SK & SL Limited | Wholesale & retail | 2021 |
| SK (UK Properties) Ltd | Real estate | 2016 |
| SK 11 Ltd | Professional & scientific | 2014 |
| SK Business Limited | Real estate | 2017 |
| SK Dave Limited | Health & social care | 2021 |
| SK Foods Watford Ltd | Hospitality | 2025 |
| SK G7 Ltd | Wholesale & retail | 2024 |
| SK Global Foods Ltd | Administrative & support | 2016 |
| SK Group 123 Ltd | Wholesale & retail | 2020 |