| Signis Holdco Limited | Financial services | 2022 |
| Signis Limited | Health & social care | 2014 |
| Sikhanda WE Care Limited | Health & social care | 2020 |
| SIL Development Limited | Real estate | 2010 |
| Silks Laser Clinic Limited | Extraterritorial | 2013 |
| Silo Cleaning Services Limited | Administrative & support | 1999 |
| Silver Lining Cloud Accountancy Limited | Professional & scientific | 2012 |
| Silver Property Homes Ltd | Construction | 2019 |
| Silver Property Services Limited | Construction | 2015 |
| Silver Star Hand Car Wash Ltd | Other services | 2026 |
| Silverbrook Property Limited | Real estate | 2023 |
| Silverbrooke Investments Limited | Real estate | 2003 |
| Silversword Support Services Ltd | Wholesale & retail | 2008 |
| Silverwood House Limited | Professional & scientific | 2022 |
| Silverwood Miners' Social Club Ltd. | Hospitality | 2013 |
| SIM 4CARE Limited | Health & social care | 2025 |
| SIM Roomz Limited | Arts & recreation | 2025 |
| Simm Conveyor Services Limited | Manufacturing | 2000 |
| Simm Vulcanising Services Limited | Professional & scientific | 1968 |
| Simmonite Developments Limited | Construction | 2016 |
| Simmonite Road 1964 Limited | Extraterritorial | 2014 |
| Simo Logistics Ltd | Wholesale & retail | 2022 |
| Simon Collier Transport Ltd | Transport & logistics | 2002 |
| Simon Hayhurst Photography Limited | Professional & scientific | 2023 |
| Simon Wilkinson Limited | Construction | 2026 |
| Simple Deco Ltd | Construction | 2018 |
| Simple Office Supplies Ltd | Wholesale & retail | 2014 |
| Simplest Solutions Limited | Health & social care | 2011 |
| Simplicity Drywall Ltd | Construction | 2018 |
| Simply Lpas & Wills Limited | Financial services | 2025 |
| Simpson & Co Builders Limited | Construction | 2016 |
| Simpson Park Management Company Limited | Households | 2018 |
| Sims & Braisby Limited | Wholesale & retail | 2017 |
| Sinbaduk Ltd | Wholesale & retail | 2020 |
| Singh Bains Properties Limited | Real estate | 2011 |
| Sinilance Creations Ltd | Professional & scientific | 2025 |
| Sinnotech Ltd | Information & communication | 2025 |
| SIP Vatii Limited | Manufacturing | 2025 |
| Sipho LLP | | 2025 |
| Siren Water Treatment Limited | Water & waste | 2022 |
| Sirimage Limited | Professional & scientific | 2006 |
| Site Accommodation Specialists Ltd | Construction | 2022 |
| Site Building Systems Ltd | Construction | 2016 |
| Site Engineering Services (West Yorkshire) Limited | Construction | 2014 |
| Site Safety Training Consultants Ltd | Education | 2013 |
| Sitesi Limited | Information & communication | 2025 |
| Sitwell Park Golf Club Limited | Construction | 1980 |
| Sivar's Barber Shop Ltd | Other services | 2025 |
| Siyam Ltd | Wholesale & retail | 2022 |
| Sizer Engineering Limited | Professional & scientific | 2019 |
| Sizer Pelleting Solutions Limited | Manufacturing | 2022 |
| Sizzlers Sandwich Shop Limited | Hospitality | 2013 |
| SJ Fabrications Limited | Wholesale & retail | 2022 |
| SJ Home Rentals Ltd | Real estate | 2017 |
| SJ Matthews Joinery Limited | Construction | 2019 |
| SJ Plumbing Limited | Construction | 2016 |
| SJC Roofing Ltd | Construction | 2019 |
| SJD Sports Coaching Ltd | Arts & recreation | 2014 |
| SJL Electrical Engineering Ltd | Manufacturing | 2023 |
| SJL0123 Ltd | Administrative & support | 2025 |
| SJM Property Development & Renting Ltd | Real estate | 2025 |
| SJR Investments Limited | Professional & scientific | 2013 |
| SJR Plastering & DRY Lining Ltd | Construction | 2023 |
| SJS Laser Cutting EOT Limited | Administrative & support | 2025 |
| SJS Laser Cutting Limited | Professional & scientific | 2012 |
| SJT Platinum Ltd | Health & social care | 2016 |
| SK Group Holdings Ltd | Financial services | 2026 |
| Skaya P Ltd | Transport & logistics | 2022 |
| Skeletots Ltd | Wholesale & retail | 2021 |
| Skelton Grange Management Company Limited | Real estate | 2024 |
| SKF. LO (Chemists) Limited | Wholesale & retail | 2002 |
| Skilled Infrastructure Resource Support Services Limited | Administrative & support | 2021 |
| Skills-Uk, Education & Training Limited | Education | 2023 |
| Skin Complexion Clinic Ltd | Other services | 2026 |
| Skinnphill Investments Ltd | Real estate | 2022 |
| Skinvade Aesthetics Limited | Other services | 2019 |
| SKN by Anya Limited | Other services | 2025 |
| SKO Kitchens Ltd | Manufacturing | 2017 |
| Skoopz Ltd | Wholesale & retail | 2026 |
| SKR Specialist Services Ltd | Construction | 2021 |
| Sky Blue Properties Limited | Real estate | 2014 |
| Sky Engineering Ltd | Real estate | 2019 |
| Sky High Marketing Ltd | Wholesale & retail | 2023 |
| Sky-High Kids Services Ltd | Education | 2025 |
| Skybyte Ltd | Other services | 2026 |
| Skyhi Creative Ltd | Professional & scientific | 2022 |
| Skyjack Projects Limited | Construction | 2014 |
| Skylark Flooring Ltd | Construction | 2011 |
| Skylark Property Lettings Limited | Real estate | 2022 |
| Skyline Building Systems Ltd | Administrative & support | 2016 |
| Skyline Systems - UK - Ltd | Construction | 2013 |
| Skyn Medical Aesthetics Ltd | Health & social care | 2024 |
| Skypass Travels Limited | Administrative & support | 2025 |
| SL Measurement Limited | Professional & scientific | 2009 |
| SL Steel City Developments Ltd | Construction | 2026 |
| SL2 (Holdings) Limited | Financial services | 2024 |
| SL2 (Squared) Limited | Construction | 2020 |
| SLA Holdings Ltd | Financial services | 2016 |
| Slate H S & E Ltd | Health & social care | 2022 |
| Slatter Properties Limited | Real estate | 2021 |