| Shrink Sleeve Limited | Wholesale & retail | 1992 |
| SHS Bloomer Ltd | Hospitality | 2017 |
| SHS Equipment Ltd | Construction | 2014 |
| SHS Realty Ltd | Real estate | 2023 |
| SHU Ltd | Professional & scientific | 2010 |
| Shubh Ridit Medical Services Ltd | Health & social care | 2016 |
| Shutters and Windows Ltd | Construction | 2023 |
| Shyne-Biz Ltd | Wholesale & retail | 2026 |
| SI Overseas Holdings Limited | Professional & scientific | 1996 |
| SIA 2001 Services Limited | Construction | 2001 |
| Sibert Solar Ltd | Manufacturing | 2018 |
| Sibley Automotive Ltd | Wholesale & retail | 2021 |
| SIC Music Limited | Information & communication | 2015 |
| Siddhababa Housing Ltd | Real estate | 2016 |
| Siderf Cons Ltd | Professional & scientific | 2023 |
| Sideways Holdings Limited | Financial services | 2019 |
| Sideways Media Limited | Information & communication | 2010 |
| Siena Films Production Ltd | Information & communication | 2025 |
| Sierpinski Development Ltd. | Information & communication | 2017 |
| Sierra Madre Investment Solutions Ltd | Financial services | 2021 |
| Sierra Madre Limited | Arts & recreation | 2008 |
| SIG Real Estate Management Ltd | Real estate | 2017 |
| Sigara Limited | Real estate | 2019 |
| Sigma Security Devices Limited | Wholesale & retail | 1979 |
| Sign FX and Graphics Ltd | Professional & scientific | 2015 |
| Signage Solutions Hub Ltd | Wholesale & retail | 2025 |
| Signal ARC Systems Ltd | Information & communication | 2025 |
| Signifier Medical Technologies Limited | Professional & scientific | 2015 |
| Signtech Paperless Solutions Ltd | Information & communication | 2013 |
| Sigtest Ltd | Professional & scientific | 2022 |
| Silcock Builders Limited | Construction | 2002 |
| Silcock Holdings South East Limited | Professional & scientific | 2010 |
| Silcock Properties (Kent) Limited | Real estate | 2022 |
| Silecroft (Ashford) Management Company Limited | Administrative & support | 1983 |
| Silent Roar Limited | Administrative & support | 2003 |
| Silked London Ltd | Wholesale & retail | 2020 |
| Silkroad Gourmet Ltd | Wholesale & retail | 2023 |
| Silver Buckles Limited | Wholesale & retail | 2009 |
| Silver Celestial Ltd | Health & social care | 2021 |
| Silver Gate Vets Ltd | Professional & scientific | 2020 |
| Silver Light Associates Limited | Professional & scientific | 2012 |
| Silver Line Cabs Limited | Transport & logistics | 2026 |
| Silver Pet Travel UK Ltd | Transport & logistics | 2026 |
| Silver Scope Media Limited | Information & communication | 2010 |
| Silver Spoon WYE Limited | Real estate | 2024 |
| Silver Star Events Ltd | Hospitality | 2010 |
| Silverback IT Ltd | Information & communication | 2016 |
| Silverline Facilities Maintenance Ltd | Construction | 2025 |
| Silverline Refurbishments Limited | Construction | 2020 |
| Silvermount Estates Limited | Real estate | 2019 |
| Silverwood Dental Limited | Health & social care | 2024 |
| SIM Agri Ltd | Agriculture & fishing | 2020 |
| SIM Social Work Solution Limited | Health & social care | 2013 |
| Simbi Limited | Construction | 2015 |
| Simbiosis Consulting Ltd | Wholesale & retail | 2020 |
| Simia Circus Ltd | Education | 2019 |
| Simia Circus School CIC | Education | 2023 |
| Simms Property Management Ltd | Households | 2021 |
| Simms Steel Works Limited | Construction | 2016 |
| Simon Beaugie Picture Frames Limited | Manufacturing | 2003 |
| Simon Furlonger Specialist Sports Cars Limited | Manufacturing | 2007 |
| Simon Furlonger Specialist Workshops Limited | Wholesale & retail | 2016 |
| Simon James Home Ltd | Manufacturing | 2026 |
| Simon Pollock & Co Ltd | Professional & scientific | 2010 |
| Simple Customer Care Ltd | Administrative & support | 2001 |
| Simple Politics Limited | Information & communication | 2015 |
| Simple Sussex Funerals Ltd | Other services | 2018 |
| Simply 4 Events Ltd | Hospitality | 2025 |
| Simply Aviation Limited | Education | 2018 |
| Simply Endodontics Limited | Health & social care | 2013 |
| Simply Ice Creams Ltd | Manufacturing | 2005 |
| Simply Naturals Limited | Wholesale & retail | 2001 |
| Simply Pawfection Ltd | Manufacturing | 2011 |
| Simply Periodontics Limited | Extraterritorial | 2024 |
| Simply Property Enterprises Limited | Construction | 2025 |
| Simply Soup Ltd | Manufacturing | 2023 |
| Simply Special Builders Limited | Construction | 2017 |
| Simply Special Homes Ltd | Real estate | 2019 |
| Simply Vocal Limited | Professional & scientific | 2024 |
| Simpson & Hall Ltd | Real estate | 2024 |
| Sims Plant Hire Ltd | Administrative & support | 2026 |
| Singh & Kaur Empire Limited | Real estate | 2026 |
| Singh Brother Cargo Limited | Transport & logistics | 2025 |
| Singleton Pizza Ltd | Hospitality | 2026 |
| Sinops Limited | Manufacturing | 1995 |
| Sinq Ltd | Information & communication | 2024 |
| SIO Brickwork Limited | Construction | 2025 |
| SIP Same Day Courier Ltd | Transport & logistics | 2025 |
| Sipra PVT Ltd | Real estate | 2019 |
| Sirenos Ltd | Administrative & support | 2026 |
| Sisi Property Limited | Real estate | 2005 |
| Sisskin Limited | Other services | 2024 |
| Site Manager 360 Ltd | Construction | 2023 |
| Sitewide Services Ltd | Professional & scientific | 2017 |
| Sithija Properties Limited | Real estate | 2024 |
| Sivano Real Estate Limited | Real estate | 2025 |
| SIX Ports Limited | Information & communication | 2017 |
| Sixfoursixfour Limited | Information & communication | 2014 |
| Sixteen Design (Kent) Limited | Professional & scientific | 2025 |
| Sixteen Twelve Developments Ltd | Real estate | 2024 |