| Shtaub and Freid Limited | Real estate | 2023 |
| Shungite Plus Ltd | Wholesale & retail | 2019 |
| SHY Lowen Care Limited | Health & social care | 2013 |
| Shyp Limited | Health & social care | 2019 |
| SI Business Consultants Ltd | Information & communication | 2025 |
| SI Business Services Limited | Information & communication | 2014 |
| Si&Hg Ltd | Households | 2025 |
| Sibley Group Ltd | Transport & logistics | 2020 |
| Sibley Material Movements Limited | Transport & logistics | 1935 |
| Sierra Charlie Ltd | Real estate | 2021 |
| Sifir IKI Ltd | Hospitality | 2026 |
| Sigart Ltd | Arts & recreation | 2019 |
| Sigma Electrical Services Limited | Manufacturing | 1999 |
| Sigma Golf (UK) Limited | Wholesale & retail | 1981 |
| Sigma Homme Limited | Wholesale & retail | 2023 |
| Sigma Telecommunications Limited | Information & communication | 2001 |
| Signal Boost UK Limited | Information & communication | 2009 |
| Signatures Mobile Bar Ltd | Other services | 2016 |
| Sikol Ltd | Information & communication | 2017 |
| Silicon Hoses.Com Ltd | Wholesale & retail | 2005 |
| Silo Brewing Company Ltd | Manufacturing | 2025 |
| Silom Limited | Professional & scientific | 1997 |
| Silvarena Ltd | Wholesale & retail | 2024 |
| Silver Birch Care Recruitment Limited | Public administration | 2019 |
| Silver FOX Lettings Ltd | Real estate | 2021 |
| Silver HCW Ltd | Wholesale & retail | 2018 |
| Silverhammer Auctions Ltd | Wholesale & retail | 2021 |
| Silverpeak Holdings Limited | Financial services | 2026 |
| Simatek Ltd | Information & communication | 2011 |
| Simir Aviation Ltd | Manufacturing | 2024 |
| Simitu Innovation (UK) Ltd | Professional & scientific | 2012 |
| Simms Auto Salvage Ltd | Wholesale & retail | 2022 |
| Simon Jones Wealth Management Limited | Financial services | 2011 |
| Simon Thompson Property Ltd | Real estate | 2026 |
| Simple Executry Trusts Limited | Professional & scientific | 2015 |
| Simplisim Limited | Information & communication | 2018 |
| Simply Eco Cleaning Services Ltd | Administrative & support | 2020 |
| Simply Gym Limited | Arts & recreation | 2011 |
| Simply Gym One Limited | Extraterritorial | 2022 |
| Simply Gym Three Limited | Extraterritorial | 2022 |
| Simply Gym Two Limited | Extraterritorial | 2022 |
| Simtrack Studios Limited | Information & communication | 2023 |
| Singel Ltd | Manufacturing | 2020 |
| Sintech.Cz Limited | Administrative & support | 2006 |
| SIP Happens Street Kitchen Ltd | Hospitality | 2026 |
| SIR Thomas Rich's School | Education | 2010 |
| Siris Engineering Services Ltd | Professional & scientific | 2022 |
| Sisu Pancakes Wholesale Ltd | Manufacturing | 2026 |
| Site Admin Services Ltd | Administrative & support | 2018 |
| Site Clean Limited | Construction | 2017 |
| Sittwell Ltd | Professional & scientific | 2018 |
| SIX Artist Management Ltd | Arts & recreation | 2011 |
| SIX Counties Concrete Pumping Ltd | Construction | 2013 |
| SIX HR Ltd | Administrative & support | 2022 |
| SIX Walls Studio Ltd | Professional & scientific | 2025 |
| SIX7LOGISTICS Ltd | Transport & logistics | 2025 |
| Sixacre SW Limited | Real estate | 2019 |
| Sixglenvilleparade Ltd | Real estate | 2021 |
| Sixoaks 2021 Limited | Administrative & support | 2021 |
| Sixpence Industries Ltd | Wholesale & retail | 2019 |
| Siza Technologies Limited | Information & communication | 2025 |
| Siznax Ltd | Wholesale & retail | 2025 |
| Sizwe Care Limited | Health & social care | 2014 |
| SJ & RA Jones Limited | Administrative & support | 2015 |
| SJ Consults Ltd | Professional & scientific | 2022 |
| SJ Lets Ltd | Households | 2019 |
| SJA Hospitality Limited | Professional & scientific | 2020 |
| SJC Property Holding Ltd | Real estate | 2017 |
| SJM Freelance Limited | Professional & scientific | 2017 |
| SJR Carpets and Flooring Limited | Wholesale & retail | 2023 |
| SJW Financial Planning Ltd | Financial services | 2011 |
| SK Ortho Ltd | Health & social care | 2019 |
| SKG Capital Investment Limited | Real estate | 2019 |
| SKI Groundworks & Construction (SW) Limited | Construction | 2023 |
| SKI Groundworks and Construction Limited | Administrative & support | 2019 |
| SKI Motors Ltd | Wholesale & retail | 2017 |
| Skimsetplastering Ltd | Construction | 2021 |
| Skin Therapy Ltd | Other services | 2023 |
| Sky Blue Paradise Ltd | Information & communication | 2026 |
| Sky Line Transport Limited | Transport & logistics | 2026 |
| Sky Summits Limited | Arts & recreation | 2018 |
| Sky Vigil Care Ltd | Health & social care | 2018 |
| Skydrivelogistics Ltd | Transport & logistics | 2025 |
| Skyfield Homes Limited | Construction | 2024 |
| Skyline Access Scaffolding Ltd | Construction | 2011 |
| Skyline Softwash EC Ltd | Administrative & support | 2025 |
| Skysight Ltd | Professional & scientific | 2024 |
| SL Clothing Limited | Manufacturing | 2005 |
| Sladeksbarber Ltd | Other services | 2026 |
| Slam 69 Ltd. | Wholesale & retail | 2010 |
| Slate and Forge Roofing Limited | Construction | 2025 |
| Slatter Electrical Limited | Construction | 2002 |
| Slbb Limited | Professional & scientific | 2017 |
| Slcsquared Ltd | Extraterritorial | 2018 |
| Sleepy Elephant Massage Ltd | Other services | 2026 |
| Slender Soles Ltd | Wholesale & retail | 2025 |
| Slimbosa Ltd | Wholesale & retail | 2018 |
| Slimbridge Health Ltd | Health & social care | 2019 |
| Slimbridge Legion Social Club Limited | Hospitality | 2011 |
| Sljr Services Limited | Administrative & support | 2026 |