| Sicambria Ltd. | Wholesale & retail | 2010 |
| Sicily Abroad Ltd | Hospitality | 2024 |
| Sidford Farms Holdings Ltd | Financial services | 2025 |
| Sidford Farms Limited | Agriculture & fishing | 1990 |
| Sidra Ltd | Health & social care | 2009 |
| Sigma-Hse (Holding) Ltd | Financial services | 2012 |
| Sigma-Hse (UK) Limited | Professional & scientific | 2009 |
| Signal Cascade Ltd | Professional & scientific | 2025 |
| Signature Taverns Ltd | Hospitality | 2026 |
| Sigz&Trax Ltd | Professional & scientific | 2024 |
| Silico Studio Ltd | Information & communication | 2021 |
| Silk BOW Accounting Consultancy Limited | Administrative & support | 2014 |
| Silk BOW Bookkeeping Limited | Professional & scientific | 2014 |
| Silk BOW Events Limited | Administrative & support | 2016 |
| Silkstead Developments Limited | Construction | 2006 |
| Silkstead Investments Limited | Financial services | 2015 |
| Silkstead Park Management Company Limited | Households | 2022 |
| Silva Advisers Limited | Professional & scientific | 2024 |
| Silver Fern Physio Limited | Extraterritorial | 2013 |
| Silver Tadpole Limited | Professional & scientific | 2019 |
| Silver Thread Films Ltd | Information & communication | 2020 |
| Silverback Strategy Limited | Information & communication | 2020 |
| Silvergold Limited | Wholesale & retail | 2018 |
| Silveroak Winchester Group Limited | Professional & scientific | 2021 |
| Silverwell Management Company Limited | Real estate | 2000 |
| Simin Productions Limited | Information & communication | 2024 |
| Simon Jones Driving School Ltd | Education | 2021 |
| Simon Stevens Associates Limited | Real estate | 2020 |
| Simple Lets Local Ltd | Real estate | 2016 |
| Simple Supply Chain Solutions Ltd | Professional & scientific | 2013 |
| Simply Skin Clinic Limited | Health & social care | 2019 |
| Sina Health & Aesthetic Ltd | Health & social care | 2018 |
| Sinclair Thomas Hitchings Property Management and Lettings Ltd | Real estate | 2006 |
| Sing WA International Industries (UK) Limited | Wholesale & retail | 2024 |
| Siochi Limited | Agriculture & fishing | 2015 |
| Sipsma 365 Ltd | Administrative & support | 2021 |
| SIR Edward Ltd | Professional & scientific | 2025 |
| Sirdiy Ltd | Construction | 2022 |
| Siren City Bars (Cheltenham) Limited | Hospitality | 2026 |
| Siren City Bars Ltd | Financial services | 2023 |
| Siren Country Pubs Limited | Hospitality | 2021 |
| Siren Craft Brew Limited | Manufacturing | 2012 |
| Sirius Co SEC Services Ltd | Professional & scientific | 2025 |
| SIX Legs Limited | Professional & scientific | 2025 |
| Sixty Seven Sports Management Ltd | Administrative & support | 2021 |
| SJC Medical Services Limited | Health & social care | 2016 |
| SJK Asset Management Limited | Real estate | 2013 |
| SJL Mechanical Services Ltd | Administrative & support | 2006 |
| SJM Property Limited | Real estate | 2017 |
| SJT Winchester Ltd | Hospitality | 2022 |
| Sjuk Limited | Real estate | 1999 |
| Skala Digital Ltd | Professional & scientific | 2023 |
| SKI Elements Limited | Administrative & support | 2010 |
| SKI Weekends Limited | Professional & scientific | 2004 |
| Skin Solace Ltd | Other services | 2020 |
| Skipper Press Limited | Arts & recreation | 2014 |
| Skocz the Builder Limited | Construction | 2022 |
| Sky Potato Group Limited | Financial services | 2017 |
| Skyline Homes (Lyndhurst) Limited | Real estate | 2015 |
| Skyline Property Consultancy Limited | Construction | 2003 |
| Skyline Retail Ltd | Wholesale & retail | 2026 |
| Sladford Homes Ltd | Real estate | 2017 |
| Sladford Ltd | Education | 2013 |
| Sladford Medical Ltd | Health & social care | 2014 |
| Sleepy Hollow Business Park (Management Company) Limited | Households | 2020 |
| Slice Productions Ltd | Arts & recreation | 2017 |
| Slimsticks Limited | Manufacturing | 2016 |
| SLM Events Ltd | Hospitality | 2024 |
| Smach Ltd | Professional & scientific | 2000 |
| Small Architecture Limited | Professional & scientific | 2014 |
| Small Pocket Video Ltd | Information & communication | 2023 |
| Smallfry Films Ltd | Information & communication | 2026 |
| Smart Energy Optimisation Limited | Professional & scientific | 2006 |
| Smart Mountains Ltd | Information & communication | 2022 |
| Smart Tracking Systems Ltd | Wholesale & retail | 2026 |
| Smart Transervice Ltd | Transport & logistics | 2018 |
| Smart Utilities Consulting Limited | Information & communication | 2016 |
| Smartest Consultancy Ltd | Information & communication | 2019 |
| Smashed Avocado RTM Company Limited | Households | 2022 |
| Smatter Consulting Limited | Professional & scientific | 2014 |
| Smdg Consulting Ltd | Professional & scientific | 2023 |
| SME Agents Limited | Information & communication | 2025 |
| Smiling COW Ltd | Professional & scientific | 2015 |
| Smith & Leggett Construction Ltd | Construction | 2015 |
| Smorgasbord Food Limited | Hospitality | 2018 |
| SN Technologies Limited | Information & communication | 2007 |
| Snow Taylor Limited | Construction | 2007 |
| Snows Office Supplies Limited | Professional & scientific | 2007 |
| Snug Estate Agents Limited | Real estate | 2020 |
| SO Morocco Limited | Administrative & support | 2016 |
| SO Simple Designs Limited | Information & communication | 2010 |
| Sober House Ltd | Hospitality | 2025 |
| Social Starlet Ltd | Professional & scientific | 2025 |
| Sock DU Jour Ltd | Wholesale & retail | 2022 |
| Sockeye Films Ltd | Information & communication | 2026 |
| Sofpave Limited | Administrative & support | 2010 |
| Software Developer Solutions Ltd | Information & communication | 2013 |
| Sohooh Ltd | Professional & scientific | 2025 |
| Soil & Stuff Limited | Wholesale & retail | 2025 |
| Soils Limited | Construction | 1982 |