| Sian Investments Limited | Real estate | 2014 |
| Sian Management Limited | Real estate | 2016 |
| Siaratransport Ltd | Transport & logistics | 2024 |
| Sibe Consultancy Limited | Professional & scientific | 2024 |
| Sidewinder Graphics Ltd | Professional & scientific | 2021 |
| Sidhu Co Transport Limited | Transport & logistics | 2020 |
| Sidhu&Co Limited | Construction | 2018 |
| Sidhu&Dhoot Estates Ltd | Real estate | 2025 |
| Sie's PIE & Mash Ltd | Hospitality | 2015 |
| Siena Designs Ltd | Manufacturing | 2019 |
| Sierra Eco Products Limited | Wholesale & retail | 2026 |
| Sighthound Consultancy Ltd | Education | 2014 |
| Sigitas Transport Ltd | Transport & logistics | 2018 |
| Sigma Building Services Limited | Construction | 2000 |
| Sigma Fire & Security Limited | Administrative & support | 2021 |
| Sigmar Homes Ltd | Real estate | 2018 |
| Sign Interior Ltd | Construction | 2015 |
| Signal Savvy Ltd | Information & communication | 2025 |
| Signature Clean London Ltd | Administrative & support | 2026 |
| Signature Group Heating and Plumbing Ltd | Construction | 2026 |
| Signature UK Holdings Ltd | Financial services | 2026 |
| Signatures IAH Aesthetics Ltd | Other services | 2026 |
| Silk and Mackman Services Limited | Administrative & support | 2001 |
| Silvana Holdings Ltd. | Real estate | 2022 |
| Silvana Ltd. | Extraterritorial | 2018 |
| Silvana's Home Designs Ltd | Construction | 2022 |
| Silvawell Holdings Ltd | Real estate | 2023 |
| Silver & Silver Services Ltd | Transport & logistics | 2019 |
| Silver Locksmiths & Carpentry Ltd | Other services | 2026 |
| Silver Spectrum Jewellery Ltd | Wholesale & retail | 2015 |
| Silver Wolf Security Limited | Professional & scientific | 2015 |
| Silveraxis Courier Limited | Transport & logistics | 2026 |
| Silverlake Property Developments Ltd | Real estate | 2024 |
| Simi's Salon Limited | Other services | 2026 |
| Simon Michelle Transport Limited | Transport & logistics | 2014 |
| Simonelish Medical Limited | Health & social care | 2009 |
| Simon’S TRT Limited | Transport & logistics | 2025 |
| Simpa Care Agency Limited | Health & social care | 2012 |
| Simple and Beautiful Limited | Wholesale & retail | 2025 |
| Simply Business, Accounts and Tax Ltd | Professional & scientific | 2018 |
| Simply Professional Group Ltd | Real estate | 2025 |
| Simply Vape Gravesend Ltd | Wholesale & retail | 2007 |
| Simplydbest Ltd | Information & communication | 2018 |
| Simpsons Car Sales Ltd | Wholesale & retail | 2022 |
| Singaye Ltd | Transport & logistics | 2006 |
| Singh Enterprises Holdings Limited | Hospitality | 2021 |
| Singh Haulage Limited | Transport & logistics | 2020 |
| Singh Travels Private Ltd | Administrative & support | 2025 |
| Singlewell Consulting Limited | Other services | 2010 |
| Singlewell Contracting Ltd | Construction | 2023 |
| Singlewell Holdings Ltd | Real estate | 2026 |
| Singlewell Limited | Construction | 2010 |
| Singlewell Property Management Ltd | Real estate | 2025 |
| Singlewell Property Solutions Limited | Hospitality | 2014 |
| Singlewell Stationery & Print Limited | Manufacturing | 2000 |
| SIP SIP Cocktails and Beers Ltd | Hospitality | 2025 |
| Siprodcom Ltd | Transport & logistics | 2017 |
| SIR Simplicity Limited | Other services | 2017 |
| Siraz Food Ltd | Wholesale & retail | 2024 |
| Sirs Group Holdings Limited | Financial services | 2023 |
| Sisihi Ltd | Professional & scientific | 2023 |
| Sisterhood School C.I.C. | Education | 2017 |
| Sisterhood Studio Limited | Professional & scientific | 2017 |
| Site Assist Services Ltd | Construction | 2025 |
| Sitex Construction Managers Ltd | Construction | 2015 |
| Sixmfg Ltd | Wholesale & retail | 2026 |
| Sizzle Guys Ltd | Hospitality | 2025 |
| SJB Transport Ltd | Transport & logistics | 2019 |
| SJC Property Rentals Ltd | Real estate | 2025 |
| SJF Environmental Limited | Professional & scientific | 2014 |
| SJN419 Limited | Real estate | 2020 |
| SJP Group Ltd. | Construction | 1993 |
| SJR Brickwork Limited | Construction | 2013 |
| SJR Support Limited | Health & social care | 2024 |
| SJS Solutions Ltd Ltd | Construction | 2026 |
| Sjswift Ltd | Professional & scientific | 2022 |
| SK Crew Services Ltd | Construction | 2026 |
| SK Fast Foods Limited | Hospitality | 2025 |
| SK HMO Ltd | Real estate | 2023 |
| SK Interpreting Agency Ltd | Professional & scientific | 2026 |
| SKA1 Limited | Hospitality | 2011 |
| Skamat UK Limited | Professional & scientific | 2015 |
| Skaya Ltd | Transport & logistics | 2026 |
| Skess Projects Ltd. | Information & communication | 2017 |
| SKG Transport Limited | Transport & logistics | 2024 |
| Skillrise Community Interest Company | Education | 2024 |
| Skillworkz Ltd | Construction | 2022 |
| Skin Dedication Training Ltd | Education | 2022 |
| Skin Illustrations Maidstone UK Ltd | Other services | 2017 |
| Skin Illustrations Sittingbourne UK Limited | Other services | 2017 |
| Skin Illustrations Whitstable UK Limited | Other services | 2017 |
| Skinsational Aesthetic Limited | Health & social care | 2023 |
| Skiparoo Ltd | Water & waste | 2021 |
| Skom Financial and Accountancy Services Limited | Professional & scientific | 2023 |
| SKR RM Ltd | Health & social care | 2022 |
| Skrypter Group Ltd | Wholesale & retail | 2025 |
| SKS Wealth Management Limited | Professional & scientific | 2021 |
| Skunkwork Group Ltd | Information & communication | 2025 |
| Sky Plumbing & Heating Ltd | Construction | 2022 |
| Sky TAC Ltd | Professional & scientific | 2013 |